From: Adhemerval Zanella Date: Tue, 27 Jan 2026 19:56:43 +0000 (+0000) Subject: math: Sync log10f with CORE-MATH X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0b949d5d575f5d024e04c38a6b054e62abd8a5ac;p=thirdparty%2Fglibc.git math: Sync log10f with CORE-MATH The performance is similar: latency master sync improvement x86_64 34.6851 32.7977 5.44% x86_64v2 34.0921 32.4295 4.88% x86_64v3 27.8292 27.6070 0.80% aarch64 11.7246 11.1351 5.03% armhf-vpfv4 13.3748 12.9055 3.51% powerpc64le 6.4036 6.5825 -2.79% reciprocal-throughput master sync improvement x86_64 10.2653 10.0437 2.16% x86_64v2 10.8432 10.7040 1.28% x86_64v3 10.9006 11.0765 -1.61% aarch64 6.6447 6.2743 5.57% armhf-vpfv4 6.8916 6.7538 2.00% powerpc64le 2.9494 2.7661 6.21% x86_64 / i686 gcc version 15.2.1 20260112. Ryzen 5900X aarch64: gcc version 15.2.1 20251105, Neoverse-N1 armv7a-vpfv4: gcc version 15.2.1 20251105, Neoverse-N1 powerpc64le: gcc version 14.2.1 20241230, POWER10 The code size is also similar. Checked on aarch64-linux-gnu, arm-linux-gnueabihf, powerpc64le-linux-gnu, i686-linux-gnu, and x86_64-linux-gnu. Reviewed-by: Paul Zimmermann --- diff --git a/SHARED-FILES b/SHARED-FILES index a4cace09ea..172c4c613b 100644 --- a/SHARED-FILES +++ b/SHARED-FILES @@ -268,7 +268,7 @@ core-math: sysdeps/ieee754/flt-32/e_gammaf_r.c # src/binary32/lgamma/lgammaf.c, revision bc385c2 sysdeps/ieee754/flt-32/e_lgammaf_r.c - # src/binary32/log10/log10f.c, revision bc385c2 + # src/binary32/log10/log10f.c, revision ebff4c43 sysdeps/ieee754/flt-32/e_log10f.c # src/binary32/sinh/sinhf.c, revision bbfabd99 sysdeps/ieee754/flt-32/e_sinhf.c diff --git a/sysdeps/ieee754/flt-32/e_log10f.c b/sysdeps/ieee754/flt-32/e_log10f.c index e9210de136..e731500ef5 100644 --- a/sysdeps/ieee754/flt-32/e_log10f.c +++ b/sysdeps/ieee754/flt-32/e_log10f.c @@ -1,9 +1,9 @@ /* Correctly-rounded radix-10 logarithm function for binary32 value. -Copyright (c) 2022-2023 Alexei Sibidanov. +Copyright (c) 2022-2026 Alexei Sibidanov. This file is part of the CORE-MATH project -project (file src/binary32/log10/log10f.c, revision bc385c2). +project (file src/binary32/log10/log10f.c, revision ebff4c43). Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal @@ -31,24 +31,29 @@ SOFTWARE. #include #include "math_config.h" +#include +#include + static __attribute__ ((noinline)) float as_special (float x) { - uint32_t ux = asuint (x); - if (ux == 0x7f800000u) - return x; /* +inf */ - uint32_t ax = ux << 1; - if (ax == 0u) + uint32_t ux = asuint (x), ax = ux<<1; + if (ax == 0u) // x = +/-0.0 /* -0.0 */ - return __math_divzerof (1); + return __math_divzerof (1); + if (ux == 0x7f800000u) + return x; // x=+inf if (ax > 0xff000000u) - return x + x; /* nan */ + return x + x; // x=nan return __math_invalidf (x); } +typedef union {double f; uint64_t u;} b64u64_u; + float __log10f (float x) { + // reciprocal of 1+i/64 (i=0..64) rounded to 29 bits static const double tr[] = { 0x1p+0, 0x1.f81f82p-1, 0x1.f07c1fp-1, 0x1.e9131acp-1, @@ -69,45 +74,47 @@ __log10f (float x) 0x1.0842108p-1, 0x1.0624dd3p-1, 0x1.041041p-1, 0x1.0204081p-1, 0.5 }; + // logarithms of the reciprocals with offset static const double tl[] = { - -0x1.d45fd6237ebe3p-47, 0x1.b947689311b6ep-8, 0x1.b5e909c96d7d5p-7, - 0x1.45f4f59ed2165p-6, 0x1.af5f92cbd8f1ep-6, 0x1.0ba01a606de8cp-5, - 0x1.3ed119b9a2b7bp-5, 0x1.714834298eec2p-5, 0x1.a30a9d98357fbp-5, - 0x1.d41d512670813p-5, 0x1.02428c0f65519p-4, 0x1.1a23444eecc3ep-4, - 0x1.31b30543f4cb4p-4, 0x1.48f3ed39bfd04p-4, 0x1.5fe8049a0e423p-4, - 0x1.769140a6aa008p-4, 0x1.8cf1836c98cb3p-4, 0x1.a30a9d55541a1p-4, - 0x1.b8de4d1ee823ep-4, 0x1.ce6e4202ca2e6p-4, 0x1.e3bc1accace07p-4, - 0x1.f8c9683b5abd4p-4, 0x1.06cbd68ca9a6ep-3, 0x1.11142f19df73p-3, - 0x1.1b3e71fa7a97fp-3, 0x1.254b4d37a46e3p-3, 0x1.2f3b6912cbf07p-3, - 0x1.390f683115886p-3, 0x1.42c7e7fffc5a8p-3, 0x1.4c65808c78d3cp-3, - 0x1.55e8c50751c55p-3, 0x1.5f52445dec3d8p-3, 0x1.68a288c3f12p-3, - 0x1.71da17bdf0d19p-3, 0x1.7af973608afd9p-3, 0x1.84011952a2579p-3, - 0x1.8cf1837a7ea6p-3, 0x1.95cb2891e43d6p-3, 0x1.9e8e7b0f869ep-3, - 0x1.a73beaa5db18dp-3, 0x1.afd3e394558d3p-3, 0x1.b856cf060d9f1p-3, - 0x1.c0c5134de1ffcp-3, 0x1.c91f1371bc99fp-3, 0x1.d1652ffcd3f53p-3, - 0x1.d997c6f635e75p-3, 0x1.e1b733ab90f3bp-3, 0x1.e9c3ceadac856p-3, - 0x1.f1bdeec43a305p-3, 0x1.f9a5e7a5fa3fep-3, 0x1.00be05ac02f2bp-2, - 0x1.04a054d81a2d4p-2, 0x1.087a0835957fbp-2, 0x1.0c4b457099517p-2, - 0x1.101431aa1fe51p-2, 0x1.13d4f08b98dd8p-2, 0x1.178da53edb892p-2, - 0x1.1b3e71e9f9d58p-2, 0x1.1ee777defdeedp-2, 0x1.2288d7b48e23bp-2, - 0x1.2622b0f52e49fp-2, 0x1.29b522a4c6314p-2, 0x1.2d404b0e30f8p-2, - 0x1.30c4478f3fbe5p-2, 0x1.34413509f7915p-2 + -0x1.2p-46, 0x1.b947689310dfap-8, 0x1.b5e909c96d11bp-7, + 0x1.45f4f59ed1e08p-6, 0x1.af5f92cbd8bc1p-6, 0x1.0ba01a606dcdep-5, + 0x1.3ed119b9a29cdp-5, 0x1.714834298ed14p-5, 0x1.a30a9d983564cp-5, + 0x1.d41d512670665p-5, 0x1.02428c0f65442p-4, 0x1.1a23444eecb67p-4, + 0x1.31b30543f4bddp-4, 0x1.48f3ed39bfc2dp-4, 0x1.5fe8049a0e34bp-4, + 0x1.769140a6a9f3p-4, 0x1.8cf1836c98bdbp-4, 0x1.a30a9d55540cap-4, + 0x1.b8de4d1ee8167p-4, 0x1.ce6e4202ca20fp-4, 0x1.e3bc1accacd3p-4, + 0x1.f8c9683b5aafdp-4, 0x1.06cbd68ca9a03p-3, 0x1.11142f19df6c5p-3, + 0x1.1b3e71fa7a913p-3, 0x1.254b4d37a4677p-3, 0x1.2f3b6912cbe9cp-3, + 0x1.390f68311581ap-3, 0x1.42c7e7fffc53dp-3, 0x1.4c65808c78cd1p-3, + 0x1.55e8c50751beap-3, 0x1.5f52445dec36cp-3, 0x1.68a288c3f1195p-3, + 0x1.71da17bdf0cadp-3, 0x1.7af973608af6ep-3, 0x1.84011952a250ep-3, + 0x1.8cf1837a7e9f4p-3, 0x1.95cb2891e436ap-3, 0x1.9e8e7b0f86974p-3, + 0x1.a73beaa5db121p-3, 0x1.afd3e39455867p-3, 0x1.b856cf060d985p-3, + 0x1.c0c5134de1f9p-3, 0x1.c91f1371bc934p-3, 0x1.d1652ffcd3ee8p-3, + 0x1.d997c6f635e09p-3, 0x1.e1b733ab90edp-3, 0x1.e9c3ceadac7ebp-3, + 0x1.f1bdeec43a29ap-3, 0x1.f9a5e7a5fa392p-3, 0x1.00be05ac02ef5p-2, + 0x1.04a054d81a29ep-2, 0x1.087a0835957c5p-2, 0x1.0c4b4570994e1p-2, + 0x1.101431aa1fe1bp-2, 0x1.13d4f08b98da2p-2, 0x1.178da53edb85cp-2, + 0x1.1b3e71e9f9d22p-2, 0x1.1ee777defdeb7p-2, 0x1.2288d7b48e205p-2, + 0x1.2622b0f52e469p-2, 0x1.29b522a4c62dep-2, 0x1.2d404b0e30f4ap-2, + 0x1.30c4478f3fbafp-2, 0x1.34413509f78dfp-2 }; + // 10^n static const union { float f; uint32_t u; } st[] = { - { 0x1p+0 }, { 0x1.4p+3 }, { 0x1.9p+6 }, { 0x1.f4p+9 }, - { 0x1.388p+13 }, { 0x1.86ap+16 }, { 0x1.e848p+19 }, { 0x1.312dp+23 }, - { 0x1.7d784p+26 }, { 0x1.dcd65p+29 }, { 0x1.2a05f2p+33 }, { 0 }, - { 0 }, { 0 }, { 0 }, { 0 } + { 0x1.2a05f2p+33 }, { 0x1.4p+3 }, { 0x1.9p+6 }, { 0 }, + { 0x1.f4p+9 }, { 0 }, { 0x1.388p+13 }, { 0x1.86ap+16 }, + { 0 }, { 0x1.e848p+19 }, { 0 }, { 0x1.312dp+23 }, + { 0x1.7d784p+26 }, { 0 }, { 0x1.dcd65p+29 }, { 0x1p+0 } }; static const double b[] = { - 0x1.bcb7b15c5a2f8p-2, -0x1.bcbb1dbb88ebap-3, 0x1.2871c39d521c6p-3 + 0x1.bcb7b15d35067p-2, -0x1.bcbb1cd29cbafp-3, 0x1.2870e2624ce4ep-3 }; static const double c[] = { @@ -115,29 +122,35 @@ __log10f (float x) -0x1.bcb7b146a14b3p-4, 0x1.63c627d5219cbp-4, -0x1.2880736c8762dp-4, 0x1.fc1ecf913961ap-5 }; + + // ln(2)/ln(10) + const double ln10 = 0x1.34413509f79ffp-2, + ln10h = 0x1.34413509f7ap-2, + ln10l = -0x1.0cee0ed4ca7e9p-54; uint32_t ux = asuint (x); - if (__glibc_unlikely (ux < (1 << 23) || ux >= 0x7f800000u)) + if (__glibc_unlikely (ux >= 0x7f800000u)) + return as_special (x); // <=-0, nan, inf + if (__glibc_unlikely (ux == st[(ux >> 24) & 0xf].u)) + { // x = 10^n + unsigned je = ((int) ux >> 23) - 126; + je = (je * 0x4d104d4) >> 28; + return je; + } + if (__glibc_unlikely (ux < 0x00800000u)) { - if (ux == 0 || ux >= 0x7f800000u) - return as_special (x); - /* subnormal */ + if (__glibc_unlikely (ux == 0u)) + return as_special (x); // x=+0 + // subnormal int n = __builtin_clz (ux) - 8; ux <<= n; ux -= n << 23; } - unsigned m = ux & ((1 << 23) - 1), j = (m + (1 << (23 - 7))) >> (23 - 6); - double ix = tr[j], l = tl[j]; int e = ((int) ux >> 23) - 127; - unsigned je = e + 1; - je = (je * 0x4d104d4) >> 28; - if (__glibc_unlikely (ux == st[je].u)) - return je; - - double tz = asdouble (((int64_t) m | ((int64_t) 1023 << 23)) << (52 - 23)); - double z = tz * ix - 1, z2 = z * z; - double r - = ((e * 0x1.34413509f79ffp-2 + l) + z * b[0]) + z2 * (b[1] + z * b[2]); - float ub = r, lb = r + 0x1.b008p-34; + int64_t m = ux & ((1 << 23) - 1), j = (m + (1 << (23 - 7))) >> (23 - 6); + double tz = asdouble ((m << (52 - 23)) | (UINT64_C(0x3ff) << 52)); + double z = tz * tr[j] - 1, z2 = z * z; + double r = ((e * ln10 + tl[j]) + z * b[0]) + z2 * (b[1] + z * b[2]); + float ub = r, lb = r + 0x1.af23fp-34; if (__glibc_unlikely (ub != lb)) { double f = z @@ -145,13 +158,13 @@ __log10f (float x) + z2 * ((c[2] + z * c[3]) + z2 * (c[4] + z * c[5] + z2 * c[6]))); - f -= 0x1.0cee0ed4ca7e9p-54 * e; - f += l - tl[0]; - double el = e * 0x1.34413509f7ap-2; + f += ln10l * e; + f += tl[j] - tl[0]; + double el = e * ln10h; r = el + f; ub = r; tz = r; - if (__glibc_unlikely (!((asuint64 (tz) & ((1 << 28) - 1))))) + if (__glibc_unlikely (!(asuint64 (tz) & ((1 << 28) - 1)))) { double dr = (el - r) + f; r += dr * 32;