mirror of git://sourceware.org/git/glibc.git
math: Simplify and optimize modff implementation
Refactor the generic implementation to use math_config.h definitions, and add an alternative one if the ABI supports truncf instructions (gated through math-use-builtins-trunc.h). The generic implementation generates similar code for x86_64, while the optimization path aarch64 (where truncf is supported as a builtin) through frintz), the improvements are: reciprocal-throughput master patch difference workload-0_1 3.0740 3.0326 1.35% workload-1_maxint 5.2231 3.0436 41.73% workload-maxint_maxfloat 4.0962 3.0551 25.42% workload-integral 3.7093 3.0612 17.47% latency master patch difference workload-0_1 3.5521 4.7313 -33.20% workload-1_maxint 6.7148 4.7314 29.54% workload-maxint_maxfloat 4.0458 4.7518 -17.45% workload-integral 3.9719 4.7427 -19.40% Checked on aarch64-linux-gnu and x86_64-linux-gnu. Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
This commit is contained in:
Adhemerval Zanella
parent
6849c5b791
commit
61cc9922f3
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@ -165,6 +165,7 @@ issignalingf_inline (float x)
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#define BIT_WIDTH 32
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#define MANTISSA_WIDTH 23
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#define EXPONENT_WIDTH 8
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#define EXPONENT_BIAS 127
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#define MANTISSA_MASK 0x007fffff
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#define EXPONENT_MASK 0x7f800000
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#define EXP_MANT_MASK 0x7fffffff
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@ -177,12 +178,24 @@ is_nan (uint32_t x)
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return (x & EXP_MANT_MASK) > EXPONENT_MASK;
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}
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static inline bool
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is_inf (uint32_t x)
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{
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return (x << 1) == (EXPONENT_MASK << 1);
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}
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static inline uint32_t
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get_mantissa (uint32_t x)
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{
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return x & MANTISSA_MASK;
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}
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static inline int
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get_exponent (uint32_t x)
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{
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return (int)((x >> MANTISSA_WIDTH & 0xff) - EXPONENT_BIAS);
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}
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/* Convert integer number X, unbiased exponent EP, and sign S to double:
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result = X * 2^(EP+1 - exponent_bias)
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@ -1,54 +1,67 @@
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/* s_modff.c -- float version of s_modf.c.
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*/
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/* Extract signed integral and fractional values.
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Copyright (C) 1993-2025 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <math.h>
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#include <math_private.h>
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#include <libm-alias-float.h>
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static const float one = 1.0;
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#include "math_config.h"
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#include <math-use-builtins-trunc.h>
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float
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__modff(float x, float *iptr)
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__modff (float x, float *iptr)
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{
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int32_t i0,j0;
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uint32_t i;
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GET_FLOAT_WORD(i0,x);
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j0 = ((i0>>23)&0xff)-0x7f; /* exponent of x */
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if(__builtin_expect(j0<23, 1)) { /* integer part in x */
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if(j0<0) { /* |x|<1 */
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SET_FLOAT_WORD(*iptr,i0&0x80000000); /* *iptr = +-0 */
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return x;
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} else {
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i = (0x007fffff)>>j0;
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if((i0&i)==0) { /* x is integral */
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uint32_t ix;
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*iptr = x;
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GET_FLOAT_WORD(ix,x);
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SET_FLOAT_WORD(x,ix&0x80000000); /* return +-0 */
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return x;
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} else {
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SET_FLOAT_WORD(*iptr,i0&(~i));
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return x - *iptr;
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}
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}
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} else { /* no fraction part */
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*iptr = x*one;
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/* We must handle NaNs separately. */
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if (j0 == 0x80 && (i0 & 0x7fffff))
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return x*one;
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SET_FLOAT_WORD(x,i0&0x80000000); /* return +-0 */
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return x;
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uint32_t t = asuint (x);
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#if USE_TRUNCF_BUILTIN
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if (is_inf (t))
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{
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*iptr = x;
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return copysignf (0.0, x);
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}
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*iptr = truncf (x);
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return copysignf (x - *iptr, x);
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#else
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int e = get_exponent (t);
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/* No fraction part. */
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if (e < MANTISSA_WIDTH)
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{
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if (e < 0)
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{
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/* |x|<1 -> *iptr = +-0 */
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*iptr = asfloat (t & SIGN_MASK);
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return x;
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}
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uint32_t i = MANTISSA_MASK >> e;
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if ((t & i) == 0)
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{
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/* x in integral, return +-0 */
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*iptr = x;
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return asfloat (t & SIGN_MASK);
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}
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*iptr = asfloat (t & ~i);
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return x - *iptr;
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}
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/* Set invalid operation for sNaN. */
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*iptr = x * 1.0f;
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if ((e == 0x80) && (t & MANTISSA_MASK))
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return *iptr;
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return asfloat (t & SIGN_MASK);
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#endif
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}
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libm_alias_float (__modf, modf)
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