modf.S revision 1.7
1 /* $NetBSD: modf.S,v 1.7 2013/09/12 15:36:16 joerg Exp $ */ 2 3 /* 4 * Copyright (c) 1992, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This software was developed by the Computer Systems Engineering group 8 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and 9 * contributed to Berkeley. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 3. Neither the name of the University nor the names of its contributors 20 * may be used to endorse or promote products derived from this software 21 * without specific prior written permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33 * SUCH DAMAGE. 34 * 35 * from: Header: modf.s,v 1.3 92/06/20 00:00:54 torek Exp 36 */ 37 38 #include <machine/asm.h> 39 #if defined(LIBC_SCCS) && !defined(lint) 40 #if 0 41 .asciz "@(#)modf.s 8.1 (Berkeley) 6/4/93" 42 #else 43 RCSID("$NetBSD: modf.S,v 1.7 2013/09/12 15:36:16 joerg Exp $") 44 #endif 45 #endif /* LIBC_SCCS and not lint */ 46 47 #include <machine/fsr.h> 48 49 /* 50 * double modf(double val, double *iptr) 51 * 52 * Returns the fractional part of `val', storing the integer part of 53 * `val' in *iptr. Both *iptr and the return value have the same sign 54 * as `val'. 55 * 56 * Method: 57 * 58 * We use the fpu's normalization hardware to compute the integer portion 59 * of the double precision argument. Sun IEEE double precision numbers 60 * have 52 bits of mantissa, 11 bits of exponent, and one bit of sign, 61 * with the sign occupying bit 31 of word 0, and the exponent bits 30:20 62 * of word 0. Thus, values >= 2^52 are by definition integers. 63 * 64 * If we take a value that is in the range [+0..2^52) and add 2^52, all 65 * of the fractional bits fall out and all of the integer bits are summed 66 * with 2^52. If we then subtract 2^52, we get those integer bits back. 67 * This must be done with rounding set to `towards 0' or `towards -inf'. 68 * `Toward -inf' fails when the value is 0 (we get -0 back).... 69 * 70 * Note that this method will work anywhere, but is machine dependent in 71 * various aspects. 72 * 73 * Stack usage: 74 * 4@[%fp - 4] saved %fsr 75 * 4@[%fp - 8] new %fsr with rounding set to `towards 0' 76 * 8@[%fp - 16] space for moving between %i and %f registers 77 * Register usage: 78 * %i0%i1 double val; 79 * %l0 scratch 80 * %l1 sign bit (0x80000000) 81 * %i2 double *iptr; 82 * %f2:f3 `magic number' 2^52, in fpu registers 83 * %f4:f5 double v, in fpu registers 84 */ 85 86 .align 8 87 Lmagic: 88 .word 0x43300000 ! sign = 0, exponent = 52 + 1023, mantissa = 0 89 .word 0 ! (i.e., .double 0r4503599627370496e+00) 90 91 L0: 92 .word 0 ! 0.0 93 .word 0 94 95 ENTRY(modf) 96 save %sp, -64-16, %sp 97 98 /* 99 * First, compute v = abs(val) by clearing sign bit, 100 * and then set up the fpu registers. This would be 101 * much easier if we could do alu operations on fpu registers! 102 */ 103 sethi %hi(0x80000000), %l1 ! sign bit 104 andn %i0, %l1, %l0 105 st %l0, [%fp - 16] 106 #ifdef __PIC__ 107 PICCY_SET(Lmagic, %l0, %o7) 108 ldd [%l0], %f2 109 #else 110 sethi %hi(Lmagic), %l0 111 ldd [%l0 + %lo(Lmagic)], %f2 112 #endif 113 st %i1, [%fp - 12] 114 ldd [%fp - 16], %f4 ! %f4:f5 = v 115 116 /* 117 * Is %f4:f5 >= %f2:f3 ? If so, it is all integer bits. 118 * It is probably less, though. 119 */ 120 fcmped %f4, %f2 121 nop ! fpop2 delay 122 fbuge Lbig ! if >= (or unordered), go out 123 nop 124 125 /* 126 * v < 2^52, so add 2^52, then subtract 2^52, but do it all 127 * with rounding set towards zero. We leave any enabled 128 * traps enabled, but change the rounding mode. This might 129 * not be so good. Oh well.... 130 */ 131 st %fsr, [%fp - 4] ! %l5 = current FSR mode 132 set FSR_RD, %l3 ! %l3 = rounding direction mask 133 ld [%fp - 4], %l5 134 set FSR_RD_RZ << FSR_RD_SHIFT, %l4 135 andn %l5, %l3, %l6 136 or %l6, %l4, %l6 ! round towards zero, please 137 and %l5, %l3, %l5 ! save original rounding mode 138 st %l6, [%fp - 8] 139 ld [%fp - 8], %fsr 140 141 faddd %f4, %f2, %f4 ! %f4:f5 += 2^52 142 fsubd %f4, %f2, %f4 ! %f4:f5 -= 2^52 143 144 /* 145 * Restore %fsr, but leave exceptions accrued. 146 */ 147 st %fsr, [%fp - 4] 148 ld [%fp - 4], %l6 149 andn %l6, %l3, %l6 ! %l6 = %fsr & ~FSR_RD; 150 or %l5, %l6, %l5 ! %l5 |= %l6; 151 st %l5, [%fp - 4] 152 ld [%fp - 4], %fsr ! restore %fsr, leaving accrued stuff 153 154 /* 155 * Now insert the original sign in %f4:f5. 156 * This is a lot of work, so it is conditional here. 157 */ 158 btst %l1, %i0 159 be 1f 160 nop 161 st %f4, [%fp - 16] 162 ld [%fp - 16], %g1 163 or %l1, %g1, %g1 164 st %g1, [%fp - 16] 165 ld [%fp - 16], %f4 166 1: 167 168 /* 169 * The value in %f4:f5 is now the integer portion of the original 170 * argument. We need to store this in *ival (%i2), subtract it 171 * from the original value argument (%i0:i1), and return the result. 172 */ 173 std %f4, [%i2] ! *ival = %f4:f5; 174 std %i0, [%fp - 16] 175 ldd [%fp - 16], %f0 ! %f0:f1 = val; 176 fsubd %f0, %f4, %f0 ! %f0:f1 -= %f4:f5; 177 ret 178 restore 179 180 Lbig: 181 /* 182 * We get here if the original comparison of %f4:f5 (v) to 183 * %f2:f3 (2^52) came out `greater or unordered'. In this 184 * case the integer part is the original value, and the 185 * fractional part is 0. 186 */ 187 #ifdef __PIC__ 188 PICCY_SET(L0, %l0, %o7) 189 std %f0, [%i2] ! *ival = val; 190 ldd [%l0], %f0 ! return 0.0; 191 #else 192 sethi %hi(L0), %l0 193 std %f0, [%i2] ! *ival = val; 194 ldd [%l0 + %lo(L0)], %f0 ! return 0.0; 195 #endif 196 ret 197 restore 198
Indexes created Fri Sep 26 20:09:58 GMT 2025