mirror of
https://github.com/jart/cosmopolitan.git
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420f889ac3
The sincosf() function is now twice as fast, thanks to ARM Limited. The same might also be true of logf() and expm1f() which have been updated.
104 lines
4.4 KiB
C
104 lines
4.4 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╚──────────────────────────────────────────────────────────────────────────────╝
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│ │
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│ Optimized Routines │
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│ Copyright (c) 1999-2022, Arm Limited. │
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│ │
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│ Permission is hereby granted, free of charge, to any person obtaining │
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│ a copy of this software and associated documentation files (the │
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│ "Software"), to deal in the Software without restriction, including │
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│ without limitation the rights to use, copy, modify, merge, publish, │
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│ distribute, sublicense, and/or sell copies of the Software, and to │
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│ permit persons to whom the Software is furnished to do so, subject to │
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│ the following conditions: │
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│ │
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│ The above copyright notice and this permission notice shall be │
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│ included in all copies or substantial portions of the Software. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, │
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│ EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF │
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│ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. │
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│ IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY │
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│ CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, │
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│ TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE │
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│ SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. │
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│ │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/intrin/likely.h"
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#include "libc/math.h"
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#include "libc/tinymath/internal.h"
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#include "libc/tinymath/logf_data.internal.h"
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asm(".ident\t\"\\n\\n\
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Optimized Routines (MIT License)\\n\
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Copyright 2022 ARM Limited\"");
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asm(".include \"libc/disclaimer.inc\"");
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/* clang-format off */
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/*
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* Single-precision log function.
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*
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* Copyright (c) 2017-2018, Arm Limited.
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* SPDX-License-Identifier: MIT
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*/
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/*
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LOGF_TABLE_BITS = 4
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LOGF_POLY_ORDER = 4
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ULP error: 0.818 (nearest rounding.)
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Relative error: 1.957 * 2^-26 (before rounding.)
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*/
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#define T __logf_data.tab
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#define A __logf_data.poly
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#define Ln2 __logf_data.ln2
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#define N (1 << LOGF_TABLE_BITS)
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#define OFF 0x3f330000
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float logf(float x)
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{
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double_t z, r, r2, y, y0, invc, logc;
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uint32_t ix, iz, tmp;
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int k, i;
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ix = asuint(x);
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/* Fix sign of zero with downward rounding when x==1. */
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if (WANT_ROUNDING && UNLIKELY(ix == 0x3f800000))
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return 0;
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if (UNLIKELY(ix - 0x00800000 >= 0x7f800000 - 0x00800000)) {
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/* x < 0x1p-126 or inf or nan. */
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if (ix * 2 == 0)
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return __math_divzerof(1);
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if (ix == 0x7f800000) /* log(inf) == inf. */
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return x;
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if ((ix & 0x80000000) || ix * 2 >= 0xff000000)
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return __math_invalidf(x);
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/* x is subnormal, normalize it. */
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ix = asuint(x * 0x1p23f);
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ix -= 23 << 23;
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}
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/* x = 2^k z; where z is in range [OFF,2*OFF] and exact.
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The range is split into N subintervals.
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The ith subinterval contains z and c is near its center. */
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tmp = ix - OFF;
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i = (tmp >> (23 - LOGF_TABLE_BITS)) % N;
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k = (int32_t)tmp >> 23; /* arithmetic shift */
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iz = ix - (tmp & 0xff800000);
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invc = T[i].invc;
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logc = T[i].logc;
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z = (double_t)asfloat(iz);
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/* log(x) = log1p(z/c-1) + log(c) + k*Ln2 */
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r = z * invc - 1;
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y0 = logc + (double_t)k * Ln2;
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/* Pipelined polynomial evaluation to approximate log1p(r). */
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r2 = r * r;
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y = A[1] * r + A[2];
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y = A[0] * r2 + y;
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y = y * r2 + (y0 + r);
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return eval_as_float(y);
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}
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