From: Adhemerval Zanella Date: Mon, 16 Jun 2025 13:17:33 +0000 (-0300) Subject: math: Simplify and optimize modff implementation X-Git-Tag: glibc-2.42~106 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=61cc9922f3cdcd71ed8977016b8180d409826240;p=thirdparty%2Fglibc.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 --- diff --git a/sysdeps/ieee754/flt-32/math_config.h b/sysdeps/ieee754/flt-32/math_config.h index fd9481a016..33ea631d5f 100644 --- a/sysdeps/ieee754/flt-32/math_config.h +++ b/sysdeps/ieee754/flt-32/math_config.h @@ -165,6 +165,7 @@ issignalingf_inline (float x) #define BIT_WIDTH 32 #define MANTISSA_WIDTH 23 #define EXPONENT_WIDTH 8 +#define EXPONENT_BIAS 127 #define MANTISSA_MASK 0x007fffff #define EXPONENT_MASK 0x7f800000 #define EXP_MANT_MASK 0x7fffffff @@ -177,12 +178,24 @@ is_nan (uint32_t x) return (x & EXP_MANT_MASK) > EXPONENT_MASK; } +static inline bool +is_inf (uint32_t x) +{ + return (x << 1) == (EXPONENT_MASK << 1); +} + static inline uint32_t get_mantissa (uint32_t x) { return x & MANTISSA_MASK; } +static inline int +get_exponent (uint32_t x) +{ + return (int)((x >> MANTISSA_WIDTH & 0xff) - EXPONENT_BIAS); +} + /* Convert integer number X, unbiased exponent EP, and sign S to double: result = X * 2^(EP+1 - exponent_bias) diff --git a/sysdeps/ieee754/flt-32/s_modff.c b/sysdeps/ieee754/flt-32/s_modff.c index ad2e91de25..e6d2e4ab49 100644 --- a/sysdeps/ieee754/flt-32/s_modff.c +++ b/sysdeps/ieee754/flt-32/s_modff.c @@ -1,54 +1,67 @@ -/* s_modff.c -- float version of s_modf.c. - */ - -/* - * ==================================================== - * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. - * - * Developed at SunPro, a Sun Microsystems, Inc. business. - * Permission to use, copy, modify, and distribute this - * software is freely granted, provided that this notice - * is preserved. - * ==================================================== - */ +/* Extract signed integral and fractional values. + Copyright (C) 1993-2025 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ #include -#include #include - -static const float one = 1.0; +#include "math_config.h" +#include float -__modff(float x, float *iptr) +__modff (float x, float *iptr) { - int32_t i0,j0; - uint32_t i; - GET_FLOAT_WORD(i0,x); - j0 = ((i0>>23)&0xff)-0x7f; /* exponent of x */ - if(__builtin_expect(j0<23, 1)) { /* integer part in x */ - if(j0<0) { /* |x|<1 */ - SET_FLOAT_WORD(*iptr,i0&0x80000000); /* *iptr = +-0 */ - return x; - } else { - i = (0x007fffff)>>j0; - if((i0&i)==0) { /* x is integral */ - uint32_t ix; - *iptr = x; - GET_FLOAT_WORD(ix,x); - SET_FLOAT_WORD(x,ix&0x80000000); /* return +-0 */ - return x; - } else { - SET_FLOAT_WORD(*iptr,i0&(~i)); - return x - *iptr; - } - } - } else { /* no fraction part */ - *iptr = x*one; - /* We must handle NaNs separately. */ - if (j0 == 0x80 && (i0 & 0x7fffff)) - return x*one; - SET_FLOAT_WORD(x,i0&0x80000000); /* return +-0 */ - return x; + uint32_t t = asuint (x); +#if USE_TRUNCF_BUILTIN + if (is_inf (t)) + { + *iptr = x; + return copysignf (0.0, x); + } + *iptr = truncf (x); + return copysignf (x - *iptr, x); +#else + int e = get_exponent (t); + /* No fraction part. */ + if (e < MANTISSA_WIDTH) + { + if (e < 0) + { + /* |x|<1 -> *iptr = +-0 */ + *iptr = asfloat (t & SIGN_MASK); + return x; } + + uint32_t i = MANTISSA_MASK >> e; + if ((t & i) == 0) + { + /* x in integral, return +-0 */ + *iptr = x; + return asfloat (t & SIGN_MASK); + } + + *iptr = asfloat (t & ~i); + return x - *iptr; + } + + /* Set invalid operation for sNaN. */ + *iptr = x * 1.0f; + if ((e == 0x80) && (t & MANTISSA_MASK)) + return *iptr; + return asfloat (t & SIGN_MASK); +#endif } libm_alias_float (__modf, modf)