xref: /xsrc/external/mit/MesaLib/dist/src/mesa/program/prog_execute.c

/*
 * Mesa 3-D graphics library
 *
 * Copyright (C) 1999-2008  Brian Paul   All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

/**
 * \file prog_execute.c
 * Software interpreter for vertex/fragment programs.
 * \author Brian Paul
 */

/*
 * NOTE: we do everything in single-precision floating point; we don't
 * currently observe the single/half/fixed-precision qualifiers.
 *
 */


#include "c99_math.h"
#include "main/errors.h"
#include "main/glheader.h"
#include "main/macros.h"
#include "main/mtypes.h"
#include "prog_execute.h"
#include "prog_instruction.h"
#include "prog_parameter.h"
#include "prog_print.h"
#include "prog_noise.h"


/* debug predicate */
#define DEBUG_PROG 0


/**
 * Set x to positive or negative infinity.
 */
#define SET_POS_INFINITY(x)                  \
   do {                                      \
         fi_type fi;                         \
         fi.i = 0x7F800000;                  \
         x = fi.f;                           \
   } while (0)
#define SET_NEG_INFINITY(x)                  \
   do {                                      \
         fi_type fi;                         \
         fi.i = 0xFF800000;                  \
         x = fi.f;                           \
   } while (0)

#define SET_FLOAT_BITS(x, bits) ((fi_type *) (void *) &(x))->i = bits


static const GLfloat ZeroVec[4] = { 0.0F, 0.0F, 0.0F, 0.0F };


/**
 * Return a pointer to the 4-element float vector specified by the given
 * source register.
 */
static inline const GLfloat *
get_src_register_pointer(const struct prog_src_register *source,
                         const struct gl_program_machine *machine)
{
   const struct gl_program *prog = machine->CurProgram;
   GLint reg = source->Index;

   if (source->RelAddr) {
      /* add address register value to src index/offset */
      reg += machine->AddressReg[0][0];
      if (reg < 0) {
         return ZeroVec;
      }
   }

   switch (source->File) {
   case PROGRAM_TEMPORARY:
      if (reg >= MAX_PROGRAM_TEMPS)
         return ZeroVec;
      return machine->Temporaries[reg];

   case PROGRAM_INPUT:
      if (prog->Target == GL_VERTEX_PROGRAM_ARB) {
         if (reg >= VERT_ATTRIB_MAX)
            return ZeroVec;
         return machine->VertAttribs[reg];
      }
      else {
         if (reg >= VARYING_SLOT_MAX)
            return ZeroVec;
         return machine->Attribs[reg][machine->CurElement];
      }

   case PROGRAM_OUTPUT:
      if (reg >= MAX_PROGRAM_OUTPUTS)
         return ZeroVec;
      return machine->Outputs[reg];

   case PROGRAM_STATE_VAR:
      FALLTHROUGH;
   case PROGRAM_CONSTANT:
      FALLTHROUGH;
   case PROGRAM_UNIFORM: {
      if (reg >= (GLint) prog->Parameters->NumParameters)
         return ZeroVec;

      unsigned pvo = prog->Parameters->Parameters[reg].ValueOffset;
      return (GLfloat *) prog->Parameters->ParameterValues + pvo;
   }
   case PROGRAM_SYSTEM_VALUE:
      assert(reg < (GLint) ARRAY_SIZE(machine->SystemValues));
      return machine->SystemValues[reg];

   default:
      _mesa_problem(NULL,
         "Invalid src register file %d in get_src_register_pointer()",
         source->File);
      return ZeroVec;
   }
}


/**
 * Return a pointer to the 4-element float vector specified by the given
 * destination register.
 */
static inline GLfloat *
get_dst_register_pointer(const struct prog_dst_register *dest,
                         struct gl_program_machine *machine)
{
   static GLfloat dummyReg[4];
   GLint reg = dest->Index;

   if (dest->RelAddr) {
      /* add address register value to src index/offset */
      reg += machine->AddressReg[0][0];
      if (reg < 0) {
         return dummyReg;
      }
   }

   switch (dest->File) {
   case PROGRAM_TEMPORARY:
      if (reg >= MAX_PROGRAM_TEMPS)
         return dummyReg;
      return machine->Temporaries[reg];

   case PROGRAM_OUTPUT:
      if (reg >= MAX_PROGRAM_OUTPUTS)
         return dummyReg;
      return machine->Outputs[reg];

   default:
      _mesa_problem(NULL,
         "Invalid dest register file %d in get_dst_register_pointer()",
         dest->File);
      return dummyReg;
   }
}



/**
 * Fetch a 4-element float vector from the given source register.
 * Apply swizzling and negating as needed.
 */
static void
fetch_vector4(const struct prog_src_register *source,
              const struct gl_program_machine *machine, GLfloat result[4])
{
   const GLfloat *src = get_src_register_pointer(source, machine);

   if (source->Swizzle == SWIZZLE_NOOP) {
      /* no swizzling */
      COPY_4V(result, src);
   }
   else {
      assert(GET_SWZ(source->Swizzle, 0) <= 3);
      assert(GET_SWZ(source->Swizzle, 1) <= 3);
      assert(GET_SWZ(source->Swizzle, 2) <= 3);
      assert(GET_SWZ(source->Swizzle, 3) <= 3);
      result[0] = src[GET_SWZ(source->Swizzle, 0)];
      result[1] = src[GET_SWZ(source->Swizzle, 1)];
      result[2] = src[GET_SWZ(source->Swizzle, 2)];
      result[3] = src[GET_SWZ(source->Swizzle, 3)];
   }

   if (source->Negate) {
      assert(source->Negate == NEGATE_XYZW);
      result[0] = -result[0];
      result[1] = -result[1];
      result[2] = -result[2];
      result[3] = -result[3];
   }

#ifdef NAN_CHECK
   assert(!util_is_inf_or_nan(result[0]));
   assert(!util_is_inf_or_nan(result[0]));
   assert(!util_is_inf_or_nan(result[0]));
   assert(!util_is_inf_or_nan(result[0]));
#endif
}


/**
 * Fetch the derivative with respect to X or Y for the given register.
 * XXX this currently only works for fragment program input attribs.
 */
static void
fetch_vector4_deriv(const struct prog_src_register *source,
                    const struct gl_program_machine *machine,
                    char xOrY, GLfloat result[4])
{
   if (source->File == PROGRAM_INPUT &&
       source->Index < (GLint) machine->NumDeriv) {
      const GLint col = machine->CurElement;
      const GLfloat w = machine->Attribs[VARYING_SLOT_POS][col][3];
      const GLfloat invQ = 1.0f / w;
      GLfloat deriv[4];

      if (xOrY == 'X') {
         deriv[0] = machine->DerivX[source->Index][0] * invQ;
         deriv[1] = machine->DerivX[source->Index][1] * invQ;
         deriv[2] = machine->DerivX[source->Index][2] * invQ;
         deriv[3] = machine->DerivX[source->Index][3] * invQ;
      }
      else {
         deriv[0] = machine->DerivY[source->Index][0] * invQ;
         deriv[1] = machine->DerivY[source->Index][1] * invQ;
         deriv[2] = machine->DerivY[source->Index][2] * invQ;
         deriv[3] = machine->DerivY[source->Index][3] * invQ;
      }

      result[0] = deriv[GET_SWZ(source->Swizzle, 0)];
      result[1] = deriv[GET_SWZ(source->Swizzle, 1)];
      result[2] = deriv[GET_SWZ(source->Swizzle, 2)];
      result[3] = deriv[GET_SWZ(source->Swizzle, 3)];

      if (source->Negate) {
         assert(source->Negate == NEGATE_XYZW);
         result[0] = -result[0];
         result[1] = -result[1];
         result[2] = -result[2];
         result[3] = -result[3];
      }
   }
   else {
      ASSIGN_4V(result, 0.0, 0.0, 0.0, 0.0);
   }
}


/**
 * As above, but only return result[0] element.
 */
static void
fetch_vector1(const struct prog_src_register *source,
              const struct gl_program_machine *machine, GLfloat result[4])
{
   const GLfloat *src = get_src_register_pointer(source, machine);

   result[0] = src[GET_SWZ(source->Swizzle, 0)];

   if (source->Negate) {
      result[0] = -result[0];
   }
}


/**
 * Fetch texel from texture.  Use partial derivatives when possible.
 */
static inline void
fetch_texel(struct gl_context *ctx,
            const struct gl_program_machine *machine,
            const struct prog_instruction *inst,
            const GLfloat texcoord[4], GLfloat lodBias,
            GLfloat color[4])
{
   const GLuint unit = machine->Samplers[inst->TexSrcUnit];

   /* Note: we only have the right derivatives for fragment input attribs.
    */
   if (machine->NumDeriv > 0 &&
       inst->SrcReg[0].File == PROGRAM_INPUT &&
       inst->SrcReg[0].Index == VARYING_SLOT_TEX0 + inst->TexSrcUnit) {
      /* simple texture fetch for which we should have derivatives */
      GLuint attr = inst->SrcReg[0].Index;
      machine->FetchTexelDeriv(ctx, texcoord,
                               machine->DerivX[attr],
                               machine->DerivY[attr],
                               lodBias, unit, color);
   }
   else {
      machine->FetchTexelLod(ctx, texcoord, lodBias, unit, color);
   }
}


/**
 * Store 4 floats into a register.  Observe the instructions saturate and
 * set-condition-code flags.
 */
static void
store_vector4(const struct prog_instruction *inst,
              struct gl_program_machine *machine, const GLfloat value[4])
{
   const struct prog_dst_register *dstReg = &(inst->DstReg);
   const GLboolean clamp = inst->Saturate;
   GLuint writeMask = dstReg->WriteMask;
   GLfloat clampedValue[4];
   GLfloat *dst = get_dst_register_pointer(dstReg, machine);

#if 0
   if (value[0] > 1.0e10 ||
       util_is_inf_or_nan(value[0]) ||
       util_is_inf_or_nan(value[1]) ||
       util_is_inf_or_nan(value[2]) || util_is_inf_or_nan(value[3]))
      printf("store %g %g %g %g\n", value[0], value[1], value[2], value[3]);
#endif

   if (clamp) {
      clampedValue[0] = CLAMP(value[0], 0.0F, 1.0F);
      clampedValue[1] = CLAMP(value[1], 0.0F, 1.0F);
      clampedValue[2] = CLAMP(value[2], 0.0F, 1.0F);
      clampedValue[3] = CLAMP(value[3], 0.0F, 1.0F);
      value = clampedValue;
   }

#ifdef NAN_CHECK
   assert(!util_is_inf_or_nan(value[0]));
   assert(!util_is_inf_or_nan(value[0]));
   assert(!util_is_inf_or_nan(value[0]));
   assert(!util_is_inf_or_nan(value[0]));
#endif

   if (writeMask & WRITEMASK_X)
      dst[0] = value[0];
   if (writeMask & WRITEMASK_Y)
      dst[1] = value[1];
   if (writeMask & WRITEMASK_Z)
      dst[2] = value[2];
   if (writeMask & WRITEMASK_W)
      dst[3] = value[3];
}


/**
 * Execute the given vertex/fragment program.
 *
 * \param ctx  rendering context
 * \param program  the program to execute
 * \param machine  machine state (must be initialized)
 * \return GL_TRUE if program completed or GL_FALSE if program executed KIL.
 */
GLboolean
_mesa_execute_program(struct gl_context * ctx,
                      const struct gl_program *program,
                      struct gl_program_machine *machine)
{
   const GLuint numInst = program->arb.NumInstructions;
   const GLuint maxExec = 65536;
   GLuint pc, numExec = 0;

   machine->CurProgram = program;

   if (DEBUG_PROG) {
      printf("execute program %u --------------------\n", program->Id);
   }

   if (program->Target == GL_VERTEX_PROGRAM_ARB) {
      machine->EnvParams = ctx->VertexProgram.Parameters;
   }
   else {
      machine->EnvParams = ctx->FragmentProgram.Parameters;
   }

   for (pc = 0; pc < numInst; pc++) {
      const struct prog_instruction *inst = program->arb.Instructions + pc;

      if (DEBUG_PROG) {
         _mesa_print_instruction(inst);
      }

      switch (inst->Opcode) {
      case OPCODE_ABS:
         {
            GLfloat a[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            result[0] = fabsf(a[0]);
            result[1] = fabsf(a[1]);
            result[2] = fabsf(a[2]);
            result[3] = fabsf(a[3]);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_ADD:
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = a[0] + b[0];
            result[1] = a[1] + b[1];
            result[2] = a[2] + b[2];
            result[3] = a[3] + b[3];
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("ADD (%g %g %g %g) = (%g %g %g %g) + (%g %g %g %g)\n",
                      result[0], result[1], result[2], result[3],
                      a[0], a[1], a[2], a[3], b[0], b[1], b[2], b[3]);
            }
         }
         break;
      case OPCODE_ARL:
         {
            GLfloat t[4];
            fetch_vector4(&inst->SrcReg[0], machine, t);
            machine->AddressReg[0][0] = util_ifloor(t[0]);
            if (DEBUG_PROG) {
               printf("ARL %d\n", machine->AddressReg[0][0]);
            }
         }
         break;
      case OPCODE_BGNLOOP:
         /* no-op */
         assert(program->arb.Instructions[inst->BranchTarget].Opcode
                == OPCODE_ENDLOOP);
         break;
      case OPCODE_ENDLOOP:
         /* subtract 1 here since pc is incremented by for(pc) loop */
         assert(program->arb.Instructions[inst->BranchTarget].Opcode
                == OPCODE_BGNLOOP);
         pc = inst->BranchTarget - 1;   /* go to matching BNGLOOP */
         break;
      case OPCODE_BGNSUB:      /* begin subroutine */
         break;
      case OPCODE_ENDSUB:      /* end subroutine */
         break;
      case OPCODE_BRK:         /* break out of loop (conditional) */
         assert(program->arb.Instructions[inst->BranchTarget].Opcode
                == OPCODE_ENDLOOP);
         /* break out of loop */
         /* pc++ at end of for-loop will put us after the ENDLOOP inst */
         pc = inst->BranchTarget;
         break;
      case OPCODE_CONT:        /* continue loop (conditional) */
         assert(program->arb.Instructions[inst->BranchTarget].Opcode
                == OPCODE_ENDLOOP);
         /* continue at ENDLOOP */
         /* Subtract 1 here since we'll do pc++ at end of for-loop */
         pc = inst->BranchTarget - 1;
         break;
      case OPCODE_CAL:         /* Call subroutine (conditional) */
         /* call the subroutine */
         if (machine->StackDepth >= MAX_PROGRAM_CALL_DEPTH) {
            return GL_TRUE;  /* Per GL_NV_vertex_program2 spec */
         }
         machine->CallStack[machine->StackDepth++] = pc + 1; /* next inst */
         /* Subtract 1 here since we'll do pc++ at end of for-loop */
         pc = inst->BranchTarget - 1;
         break;
      case OPCODE_CMP:
         {
            GLfloat a[4], b[4], c[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            fetch_vector4(&inst->SrcReg[2], machine, c);
            result[0] = a[0] < 0.0F ? b[0] : c[0];
            result[1] = a[1] < 0.0F ? b[1] : c[1];
            result[2] = a[2] < 0.0F ? b[2] : c[2];
            result[3] = a[3] < 0.0F ? b[3] : c[3];
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("CMP (%g %g %g %g) = (%g %g %g %g) < 0 ? (%g %g %g %g) : (%g %g %g %g)\n",
                      result[0], result[1], result[2], result[3],
                      a[0], a[1], a[2], a[3],
                      b[0], b[1], b[2], b[3],
                      c[0], c[1], c[2], c[3]);
            }
         }
         break;
      case OPCODE_COS:
         {
            GLfloat a[4], result[4];
            fetch_vector1(&inst->SrcReg[0], machine, a);
            result[0] = result[1] = result[2] = result[3]
               = cosf(a[0]);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_DDX:         /* Partial derivative with respect to X */
         {
            GLfloat result[4];
            fetch_vector4_deriv(&inst->SrcReg[0], machine, 'X', result);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_DDY:         /* Partial derivative with respect to Y */
         {
            GLfloat result[4];
            fetch_vector4_deriv(&inst->SrcReg[0], machine, 'Y', result);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_DP2:
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = result[1] = result[2] = result[3] = DOT2(a, b);
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("DP2 %g = (%g %g) . (%g %g)\n",
                      result[0], a[0], a[1], b[0], b[1]);
            }
         }
         break;
      case OPCODE_DP3:
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = result[1] = result[2] = result[3] = DOT3(a, b);
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("DP3 %g = (%g %g %g) . (%g %g %g)\n",
                      result[0], a[0], a[1], a[2], b[0], b[1], b[2]);
            }
         }
         break;
      case OPCODE_DP4:
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = result[1] = result[2] = result[3] = DOT4(a, b);
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("DP4 %g = (%g, %g %g %g) . (%g, %g %g %g)\n",
                      result[0], a[0], a[1], a[2], a[3],
                      b[0], b[1], b[2], b[3]);
            }
         }
         break;
      case OPCODE_DPH:
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = result[1] = result[2] = result[3] = DOT3(a, b) + b[3];
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_DST:         /* Distance vector */
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = 1.0F;
            result[1] = a[1] * b[1];
            result[2] = a[2];
            result[3] = b[3];
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_EXP:
         {
            GLfloat t[4], q[4], floor_t0;
            fetch_vector1(&inst->SrcReg[0], machine, t);
            floor_t0 = floorf(t[0]);
            if (floor_t0 > FLT_MAX_EXP) {
               SET_POS_INFINITY(q[0]);
               SET_POS_INFINITY(q[2]);
            }
            else if (floor_t0 < FLT_MIN_EXP) {
               q[0] = 0.0F;
               q[2] = 0.0F;
            }
            else {
               q[0] = ldexpf(1.0, (int) floor_t0);
               /* Note: GL_NV_vertex_program expects
                * result.z = result.x * APPX(result.y)
                * We do what the ARB extension says.
                */
               q[2] = exp2f(t[0]);
            }
            q[1] = t[0] - floor_t0;
            q[3] = 1.0F;
            store_vector4( inst, machine, q );
         }
         break;
      case OPCODE_EX2:         /* Exponential base 2 */
         {
            GLfloat a[4], result[4], val;
            fetch_vector1(&inst->SrcReg[0], machine, a);
            val = exp2f(a[0]);
            /*
            if (util_is_inf_or_nan(val))
               val = 1.0e10;
            */
            result[0] = result[1] = result[2] = result[3] = val;
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_FLR:
         {
            GLfloat a[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            result[0] = floorf(a[0]);
            result[1] = floorf(a[1]);
            result[2] = floorf(a[2]);
            result[3] = floorf(a[3]);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_FRC:
         {
            GLfloat a[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            result[0] = a[0] - floorf(a[0]);
            result[1] = a[1] - floorf(a[1]);
            result[2] = a[2] - floorf(a[2]);
            result[3] = a[3] - floorf(a[3]);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_IF:
         {
            GLboolean cond;
            assert(program->arb.Instructions[inst->BranchTarget].Opcode
                   == OPCODE_ELSE ||
                   program->arb.Instructions[inst->BranchTarget].Opcode
                   == OPCODE_ENDIF);
            /* eval condition */
            GLfloat a[4];
            fetch_vector1(&inst->SrcReg[0], machine, a);
            cond = (a[0] != 0.0F);
            if (DEBUG_PROG) {
               printf("IF: %d\n", cond);
            }
            /* do if/else */
            if (cond) {
               /* do if-clause (just continue execution) */
            }
            else {
               /* go to the instruction after ELSE or ENDIF */
               assert(inst->BranchTarget >= 0);
               pc = inst->BranchTarget;
            }
         }
         break;
      case OPCODE_ELSE:
         /* goto ENDIF */
         assert(program->arb.Instructions[inst->BranchTarget].Opcode
                == OPCODE_ENDIF);
         assert(inst->BranchTarget >= 0);
         pc = inst->BranchTarget;
         break;
      case OPCODE_ENDIF:
         /* nothing */
         break;
      case OPCODE_KIL:         /* ARB_f_p only */
         {
            GLfloat a[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            if (DEBUG_PROG) {
               printf("KIL if (%g %g %g %g) <= 0.0\n",
                      a[0], a[1], a[2], a[3]);
            }

            if (a[0] < 0.0F || a[1] < 0.0F || a[2] < 0.0F || a[3] < 0.0F) {
               return GL_FALSE;
            }
         }
         break;
      case OPCODE_LG2:         /* log base 2 */
         {
            GLfloat a[4], result[4], val;
            fetch_vector1(&inst->SrcReg[0], machine, a);
	    /* The fast LOG2 macro doesn't meet the precision requirements.
	     */
            if (a[0] == 0.0F) {
               val = -FLT_MAX;
            }
            else {
               val = logf(a[0]) * 1.442695F;
            }
            result[0] = result[1] = result[2] = result[3] = val;
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_LIT:
         {
            const GLfloat epsilon = 1.0F / 256.0F;      /* from NV VP spec */
            GLfloat a[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            a[0] = MAX2(a[0], 0.0F);
            a[1] = MAX2(a[1], 0.0F);
            /* XXX ARB version clamps a[3], NV version doesn't */
            a[3] = CLAMP(a[3], -(128.0F - epsilon), (128.0F - epsilon));
            result[0] = 1.0F;
            result[1] = a[0];
            /* XXX we could probably just use pow() here */
            if (a[0] > 0.0F) {
               if (a[1] == 0.0F && a[3] == 0.0F)
                  result[2] = 1.0F;
               else
                  result[2] = powf(a[1], a[3]);
            }
            else {
               result[2] = 0.0F;
            }
            result[3] = 1.0F;
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("LIT (%g %g %g %g) : (%g %g %g %g)\n",
                      result[0], result[1], result[2], result[3],
                      a[0], a[1], a[2], a[3]);
            }
         }
         break;
      case OPCODE_LOG:
         {
            GLfloat t[4], q[4], abs_t0;
            fetch_vector1(&inst->SrcReg[0], machine, t);
            abs_t0 = fabsf(t[0]);
            if (abs_t0 != 0.0F) {
               if (util_is_inf_or_nan(abs_t0))
               {
                  SET_POS_INFINITY(q[0]);
                  q[1] = 1.0F;
                  SET_POS_INFINITY(q[2]);
               }
               else {
                  int exponent;
                  GLfloat mantissa = frexpf(t[0], &exponent);
                  q[0] = (GLfloat) (exponent - 1);
                  q[1] = 2.0F * mantissa; /* map [.5, 1) -> [1, 2) */

		  /* The fast LOG2 macro doesn't meet the precision
		   * requirements.
		   */
                  q[2] = logf(t[0]) * 1.442695F;
               }
            }
            else {
               SET_NEG_INFINITY(q[0]);
               q[1] = 1.0F;
               SET_NEG_INFINITY(q[2]);
            }
            q[3] = 1.0;
            store_vector4(inst, machine, q);
         }
         break;
      case OPCODE_LRP:
         {
            GLfloat a[4], b[4], c[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            fetch_vector4(&inst->SrcReg[2], machine, c);
            result[0] = a[0] * b[0] + (1.0F - a[0]) * c[0];
            result[1] = a[1] * b[1] + (1.0F - a[1]) * c[1];
            result[2] = a[2] * b[2] + (1.0F - a[2]) * c[2];
            result[3] = a[3] * b[3] + (1.0F - a[3]) * c[3];
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("LRP (%g %g %g %g) = (%g %g %g %g), "
                      "(%g %g %g %g), (%g %g %g %g)\n",
                      result[0], result[1], result[2], result[3],
                      a[0], a[1], a[2], a[3],
                      b[0], b[1], b[2], b[3], c[0], c[1], c[2], c[3]);
            }
         }
         break;
      case OPCODE_MAD:
         {
            GLfloat a[4], b[4], c[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            fetch_vector4(&inst->SrcReg[2], machine, c);
            result[0] = a[0] * b[0] + c[0];
            result[1] = a[1] * b[1] + c[1];
            result[2] = a[2] * b[2] + c[2];
            result[3] = a[3] * b[3] + c[3];
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("MAD (%g %g %g %g) = (%g %g %g %g) * "
                      "(%g %g %g %g) + (%g %g %g %g)\n",
                      result[0], result[1], result[2], result[3],
                      a[0], a[1], a[2], a[3],
                      b[0], b[1], b[2], b[3], c[0], c[1], c[2], c[3]);
            }
         }
         break;
      case OPCODE_MAX:
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = MAX2(a[0], b[0]);
            result[1] = MAX2(a[1], b[1]);
            result[2] = MAX2(a[2], b[2]);
            result[3] = MAX2(a[3], b[3]);
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("MAX (%g %g %g %g) = (%g %g %g %g), (%g %g %g %g)\n",
                      result[0], result[1], result[2], result[3],
                      a[0], a[1], a[2], a[3], b[0], b[1], b[2], b[3]);
            }
         }
         break;
      case OPCODE_MIN:
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = MIN2(a[0], b[0]);
            result[1] = MIN2(a[1], b[1]);
            result[2] = MIN2(a[2], b[2]);
            result[3] = MIN2(a[3], b[3]);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_MOV:
         {
            GLfloat result[4];
            fetch_vector4(&inst->SrcReg[0], machine, result);
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("MOV (%g %g %g %g)\n",
                      result[0], result[1], result[2], result[3]);
            }
         }
         break;
      case OPCODE_MUL:
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = a[0] * b[0];
            result[1] = a[1] * b[1];
            result[2] = a[2] * b[2];
            result[3] = a[3] * b[3];
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("MUL (%g %g %g %g) = (%g %g %g %g) * (%g %g %g %g)\n",
                      result[0], result[1], result[2], result[3],
                      a[0], a[1], a[2], a[3], b[0], b[1], b[2], b[3]);
            }
         }
         break;
      case OPCODE_NOISE1:
         {
            GLfloat a[4], result[4];
            fetch_vector1(&inst->SrcReg[0], machine, a);
            result[0] =
               result[1] =
               result[2] =
               result[3] = _mesa_noise1(a[0]);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_NOISE2:
         {
            GLfloat a[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            result[0] =
               result[1] =
               result[2] = result[3] = _mesa_noise2(a[0], a[1]);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_NOISE3:
         {
            GLfloat a[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            result[0] =
               result[1] =
               result[2] =
               result[3] = _mesa_noise3(a[0], a[1], a[2]);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_NOISE4:
         {
            GLfloat a[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            result[0] =
               result[1] =
               result[2] =
               result[3] = _mesa_noise4(a[0], a[1], a[2], a[3]);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_NOP:
         break;
      case OPCODE_POW:
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector1(&inst->SrcReg[0], machine, a);
            fetch_vector1(&inst->SrcReg[1], machine, b);
            result[0] = result[1] = result[2] = result[3]
               = powf(a[0], b[0]);
            store_vector4(inst, machine, result);
         }
         break;

      case OPCODE_RCP:
         {
            GLfloat a[4], result[4];
            fetch_vector1(&inst->SrcReg[0], machine, a);
            if (DEBUG_PROG) {
               if (a[0] == 0)
                  printf("RCP(0)\n");
               else if (util_is_inf_or_nan(a[0]))
                  printf("RCP(inf)\n");
            }
            result[0] = result[1] = result[2] = result[3] = 1.0F / a[0];
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_RET:         /* return from subroutine (conditional) */
         if (machine->StackDepth == 0) {
            return GL_TRUE;  /* Per GL_NV_vertex_program2 spec */
         }
         /* subtract one because of pc++ in the for loop */
         pc = machine->CallStack[--machine->StackDepth] - 1;
         break;
      case OPCODE_RSQ:         /* 1 / sqrt() */
         {
            GLfloat a[4], result[4];
            fetch_vector1(&inst->SrcReg[0], machine, a);
            a[0] = fabsf(a[0]);
            result[0] = result[1] = result[2] = result[3] = 1.0f / sqrtf(a[0]);
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("RSQ %g = 1/sqrt(|%g|)\n", result[0], a[0]);
            }
         }
         break;
      case OPCODE_SCS:         /* sine and cos */
         {
            GLfloat a[4], result[4];
            fetch_vector1(&inst->SrcReg[0], machine, a);
            result[0] = cosf(a[0]);
            result[1] = sinf(a[0]);
            result[2] = 0.0F;    /* undefined! */
            result[3] = 0.0F;    /* undefined! */
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_SGE:         /* set on greater or equal */
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = (a[0] >= b[0]) ? 1.0F : 0.0F;
            result[1] = (a[1] >= b[1]) ? 1.0F : 0.0F;
            result[2] = (a[2] >= b[2]) ? 1.0F : 0.0F;
            result[3] = (a[3] >= b[3]) ? 1.0F : 0.0F;
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("SGE (%g %g %g %g) = (%g %g %g %g) >= (%g %g %g %g)\n",
                      result[0], result[1], result[2], result[3],
                      a[0], a[1], a[2], a[3],
                      b[0], b[1], b[2], b[3]);
            }
         }
         break;
      case OPCODE_SIN:
         {
            GLfloat a[4], result[4];
            fetch_vector1(&inst->SrcReg[0], machine, a);
            result[0] = result[1] = result[2] = result[3]
               = sinf(a[0]);
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_SLT:         /* set on less */
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = (a[0] < b[0]) ? 1.0F : 0.0F;
            result[1] = (a[1] < b[1]) ? 1.0F : 0.0F;
            result[2] = (a[2] < b[2]) ? 1.0F : 0.0F;
            result[3] = (a[3] < b[3]) ? 1.0F : 0.0F;
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("SLT (%g %g %g %g) = (%g %g %g %g) < (%g %g %g %g)\n",
                      result[0], result[1], result[2], result[3],
                      a[0], a[1], a[2], a[3],
                      b[0], b[1], b[2], b[3]);
            }
         }
         break;
      case OPCODE_SSG:         /* set sign (-1, 0 or +1) */
         {
            GLfloat a[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            result[0] = (GLfloat) ((a[0] > 0.0F) - (a[0] < 0.0F));
            result[1] = (GLfloat) ((a[1] > 0.0F) - (a[1] < 0.0F));
            result[2] = (GLfloat) ((a[2] > 0.0F) - (a[2] < 0.0F));
            result[3] = (GLfloat) ((a[3] > 0.0F) - (a[3] < 0.0F));
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_SUB:
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = a[0] - b[0];
            result[1] = a[1] - b[1];
            result[2] = a[2] - b[2];
            result[3] = a[3] - b[3];
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("SUB (%g %g %g %g) = (%g %g %g %g) - (%g %g %g %g)\n",
                      result[0], result[1], result[2], result[3],
                      a[0], a[1], a[2], a[3], b[0], b[1], b[2], b[3]);
            }
         }
         break;
      case OPCODE_SWZ:         /* extended swizzle */
         {
            const struct prog_src_register *source = &inst->SrcReg[0];
            const GLfloat *src = get_src_register_pointer(source, machine);
            GLfloat result[4];
            GLuint i;
            for (i = 0; i < 4; i++) {
               const GLuint swz = GET_SWZ(source->Swizzle, i);
               if (swz == SWIZZLE_ZERO)
                  result[i] = 0.0;
               else if (swz == SWIZZLE_ONE)
                  result[i] = 1.0;
               else {
                  assert(swz <= 3);
                  result[i] = src[swz];
               }
               if (source->Negate & (1 << i))
                  result[i] = -result[i];
            }
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_TEX:         /* Both ARB and NV frag prog */
         /* Simple texel lookup */
         {
            GLfloat texcoord[4], color[4];
            fetch_vector4(&inst->SrcReg[0], machine, texcoord);

            /* For TEX, texcoord.Q should not be used and its value should not
             * matter (at most, we pass coord.xyz to texture3D() in GLSL).
             * Set Q=1 so that FetchTexelDeriv() doesn't get a garbage value
             * which is effectively what happens when the texcoord swizzle
             * is .xyzz
             */
            texcoord[3] = 1.0f;

            fetch_texel(ctx, machine, inst, texcoord, 0.0, color);

            if (DEBUG_PROG) {
               printf("TEX (%g, %g, %g, %g) = texture[%d][%g, %g, %g, %g]\n",
                      color[0], color[1], color[2], color[3],
                      inst->TexSrcUnit,
                      texcoord[0], texcoord[1], texcoord[2], texcoord[3]);
            }
            store_vector4(inst, machine, color);
         }
         break;
      case OPCODE_TXB:         /* GL_ARB_fragment_program only */
         /* Texel lookup with LOD bias */
         {
            GLfloat texcoord[4], color[4], lodBias;

            fetch_vector4(&inst->SrcReg[0], machine, texcoord);

            /* texcoord[3] is the bias to add to lambda */
            lodBias = texcoord[3];

            fetch_texel(ctx, machine, inst, texcoord, lodBias, color);

            if (DEBUG_PROG) {
               printf("TXB (%g, %g, %g, %g) = texture[%d][%g %g %g %g]"
                      "  bias %g\n",
                      color[0], color[1], color[2], color[3],
                      inst->TexSrcUnit,
                      texcoord[0],
                      texcoord[1],
                      texcoord[2],
                      texcoord[3],
                      lodBias);
            }

            store_vector4(inst, machine, color);
         }
         break;
      case OPCODE_TXD:
         /* Texture lookup w/ partial derivatives for LOD */
         {
            GLfloat texcoord[4], dtdx[4], dtdy[4], color[4];
            fetch_vector4(&inst->SrcReg[0], machine, texcoord);
            fetch_vector4(&inst->SrcReg[1], machine, dtdx);
            fetch_vector4(&inst->SrcReg[2], machine, dtdy);
            machine->FetchTexelDeriv(ctx, texcoord, dtdx, dtdy,
                                     0.0, /* lodBias */
                                     inst->TexSrcUnit, color);
            store_vector4(inst, machine, color);
         }
         break;
      case OPCODE_TXL:
         /* Texel lookup with explicit LOD */
         {
            GLfloat texcoord[4], color[4], lod;

            fetch_vector4(&inst->SrcReg[0], machine, texcoord);

            /* texcoord[3] is the LOD */
            lod = texcoord[3];

	    machine->FetchTexelLod(ctx, texcoord, lod,
				   machine->Samplers[inst->TexSrcUnit], color);

            store_vector4(inst, machine, color);
         }
         break;
      case OPCODE_TXP:         /* GL_ARB_fragment_program only */
         /* Texture lookup w/ projective divide */
         {
            GLfloat texcoord[4], color[4];

            fetch_vector4(&inst->SrcReg[0], machine, texcoord);
            /* Not so sure about this test - if texcoord[3] is
             * zero, we'd probably be fine except for an assert in
             * IROUND_POS() which gets triggered by the inf values created.
             */
            if (texcoord[3] != 0.0F) {
               texcoord[0] /= texcoord[3];
               texcoord[1] /= texcoord[3];
               texcoord[2] /= texcoord[3];
            }

            fetch_texel(ctx, machine, inst, texcoord, 0.0, color);

            store_vector4(inst, machine, color);
         }
         break;
      case OPCODE_TRUNC:       /* truncate toward zero */
         {
            GLfloat a[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            result[0] = (GLfloat) (GLint) a[0];
            result[1] = (GLfloat) (GLint) a[1];
            result[2] = (GLfloat) (GLint) a[2];
            result[3] = (GLfloat) (GLint) a[3];
            store_vector4(inst, machine, result);
         }
         break;
      case OPCODE_XPD:         /* cross product */
         {
            GLfloat a[4], b[4], result[4];
            fetch_vector4(&inst->SrcReg[0], machine, a);
            fetch_vector4(&inst->SrcReg[1], machine, b);
            result[0] = a[1] * b[2] - a[2] * b[1];
            result[1] = a[2] * b[0] - a[0] * b[2];
            result[2] = a[0] * b[1] - a[1] * b[0];
            result[3] = 1.0;
            store_vector4(inst, machine, result);
            if (DEBUG_PROG) {
               printf("XPD (%g %g %g %g) = (%g %g %g) X (%g %g %g)\n",
                      result[0], result[1], result[2], result[3],
                      a[0], a[1], a[2], b[0], b[1], b[2]);
            }
         }
         break;
      case OPCODE_END:
         return GL_TRUE;
      default:
         _mesa_problem(ctx, "Bad opcode %d in _mesa_execute_program",
                       inst->Opcode);
         return GL_TRUE;        /* return value doesn't matter */
      }

      numExec++;
      if (numExec > maxExec) {
	 static GLboolean reported = GL_FALSE;
	 if (!reported) {
	    _mesa_problem(ctx, "Infinite loop detected in fragment program");
	    reported = GL_TRUE;
	 }
         return GL_TRUE;
      }

   } /* for pc */

   return GL_TRUE;
}