1 /* $NetBSD: modf.S,v 1.5 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 1.5 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 + BIAS - 4] saved %fsr 75 * 4@[%fp + BIAS - 8] new %fsr with rounding set to `towards 0' 76 * 8@[%fp + BIAS - 16] space for moving between %i and %f registers 77 * Register usage: 78 * %f0:f1 double val; 79 * %l0 scratch 80 * %l1 sign bit (0x80000000) 81 * %i1 double *iptr; 82 * %f2:f3 `magic number' 2^52, in fpu registers 83 * %f4:f5 double v, in fpu registers 84 * %f6:f7 double temp. 85 */ 86 87 .align 8 88 Lmagic: 89 .word 0x43300000 ! sign = 0, exponent = 52 + 1023, mantissa = 0 90 .word 0 ! (i.e., .double 0r4503599627370496e+00) 91 92 L0: 93 .word 0 ! 0.0 94 .word 0 95 96 ENTRY(modf) 97 save %sp, -CC64FSZ-16, %sp 98 99 /* 100 * First, compute v = abs(val) 101 */ 102 fabsd %f0, %f4 ! %f4:f5 = v 103 fcmped %fcc1, %f0, %f4 ! %fcc1 = (val == abs(val)) 104 #ifdef __PIC__ 105 PICCY_SET(Lmagic, %l0, %o7) 106 ldd [%l0], %f2 107 #else 108 sethi %hi(Lmagic), %l0 109 ldd [%l0 + %lo(Lmagic)], %f2 110 #endif 111 112 /* 113 * Is %f4:f5 >= %f2:f3 ? If so, it is all integer bits. 114 * It is probably less, though. 115 */ 116 fcmped %f4, %f2 117 fbuge Lbig ! if >= (or unordered), go out 118 nop 119 120 /* 121 * v < 2^52, so add 2^52, then subtract 2^52, but do it all 122 * with rounding set towards zero. We leave any enabled 123 * traps enabled, but change the rounding mode. This might 124 * not be so good. Oh well.... 125 */ 126 st %fsr, [%fp + BIAS - 4] ! %l5 = current FSR mode 127 set FSR_RD, %l3 ! %l3 = rounding direction mask 128 ld [%fp + BIAS - 4], %l5 129 set FSR_RD_RZ << FSR_RD_SHIFT, %l4 130 andn %l5, %l3, %l6 131 or %l6, %l4, %l6 ! round towards zero, please 132 and %l5, %l3, %l5 ! save original rounding mode 133 st %l6, [%fp + BIAS - 8] 134 ld [%fp + BIAS - 8], %fsr 135 136 faddd %f4, %f2, %f4 ! %f4:f5 += 2^52 137 fsubd %f4, %f2, %f4 ! %f4:f5 -= 2^52 138 139 /* 140 * Restore %fsr, but leave exceptions accrued. 141 */ 142 st %fsr, [%fp + BIAS - 4] 143 ld [%fp + BIAS - 4], %l6 144 andn %l6, %l3, %l6 ! %l6 = %fsr & ~FSR_RD; 145 or %l5, %l6, %l5 ! %l5 |= %l6; 146 st %l5, [%fp + BIAS - 4] 147 ld [%fp + BIAS - 4], %fsr ! restore %fsr, leaving accrued stuff 148 149 /* 150 * Now insert the original sign in %f4:f5. 151 * %fcc1 should still have the reults of (val == abs(val)) 152 * from above, so we use a conditional move on %fcc1 to: 153 * 154 * %f4 = (val == abs(val)) ? %f4 : -%f4 155 * 156 */ 157 fnegd %f4, %f6 158 fmovdnz %fcc1, %f6, %f4 159 1: 160 161 /* 162 * The value in %f4:f5 is now the integer portion of the original 163 * argument. We need to store this in *ival (%i1), subtract it 164 * from the original value argument (%d0), and return the result. 165 */ 166 std %f4, [%i1] ! *ival = %f4:f5; 167 fsubd %f0, %f4, %f0 ! %f0:f1 -= %f4:f5; 168 ret 169 restore 170 171 Lbig: 172 /* 173 * We get here if the original comparison of %f4:f5 (v) to 174 * %f2:f3 (2^52) came out `greater or unordered'. In this 175 * case the integer part is the original value, and the 176 * fractional part is 0. 177 */ 178 #ifdef __PIC__ 179 PICCY_SET(L0, %l0, %o7) 180 std %f0, [%i1] ! *ival = val; 181 ldd [%l0], %f0 ! return 0.0; 182 #else 183 sethi %hi(L0), %l0 184 std %f0, [%i1] ! *ival = val; 185 ldd [%l0 + %lo(L0)], %f0 ! return 0.0; 186 #endif 187 ret 188 restore 189 190
Indexes created Mon Sep 22 05:09:51 GMT 2025