diff options
Diffstat (limited to 'pl/math/sv_log10f_3u5.c')
-rw-r--r-- | pl/math/sv_log10f_3u5.c | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/pl/math/sv_log10f_3u5.c b/pl/math/sv_log10f_3u5.c new file mode 100644 index 0000000..e7b1e98 --- /dev/null +++ b/pl/math/sv_log10f_3u5.c @@ -0,0 +1,88 @@ +/* + * Single-precision SVE log10 function. + * + * Copyright (c) 2022-2023, Arm Limited. + * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception + */ + +#include "sv_math.h" +#include "pl_sig.h" +#include "pl_test.h" + +#if SV_SUPPORTED + +#define SpecialCaseMin 0x00800000 +#define SpecialCaseMax 0x7f800000 +#define Offset 0x3f2aaaab /* 0.666667. */ +#define Mask 0x007fffff +#define Ln2 0x1.62e43p-1f /* 0x3f317218. */ +#define InvLn10 0x1.bcb7b2p-2f + +#define P(i) __v_log10f_poly[i] + +static NOINLINE sv_f32_t +special_case (sv_f32_t x, sv_f32_t y, svbool_t special) +{ + return sv_call_f32 (log10f, x, y, special); +} + +/* Optimised implementation of SVE log10f using the same algorithm and + polynomial as v_log10f. Maximum error is 3.31ulps: + __sv_log10f(0x1.555c16p+0) got 0x1.ffe2fap-4 + want 0x1.ffe2f4p-4. */ +sv_f32_t +__sv_log10f_x (sv_f32_t x, const svbool_t pg) +{ + sv_u32_t ix = sv_as_u32_f32 (x); + svbool_t special_cases + = svcmpge_n_u32 (pg, svsub_n_u32_x (pg, ix, SpecialCaseMin), + SpecialCaseMax - SpecialCaseMin); + + /* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */ + ix = svsub_n_u32_x (pg, ix, Offset); + sv_f32_t n = sv_to_f32_s32_x (pg, svasr_n_s32_x (pg, sv_as_s32_u32 (ix), + 23)); /* signextend. */ + ix = svand_n_u32_x (pg, ix, Mask); + ix = svadd_n_u32_x (pg, ix, Offset); + sv_f32_t r = svsub_n_f32_x (pg, sv_as_f32_u32 (ix), 1.0f); + + /* y = log10(1+r) + n*log10(2) + log10(1+r) ~ r * InvLn(10) + P(r) + where P(r) is a polynomial. Use order 9 for log10(1+x), i.e. order 8 for + log10(1+x)/x, with x in [-1/3, 1/3] (offset=2/3) + + P(r) = r2 * (Q01 + r2 * (Q23 + r2 * (Q45 + r2 * Q67))) + and Qij = Pi + r * Pj. */ + sv_f32_t q12 = sv_fma_n_f32_x (pg, P (1), r, sv_f32 (P (0))); + sv_f32_t q34 = sv_fma_n_f32_x (pg, P (3), r, sv_f32 (P (2))); + sv_f32_t q56 = sv_fma_n_f32_x (pg, P (5), r, sv_f32 (P (4))); + sv_f32_t q78 = sv_fma_n_f32_x (pg, P (7), r, sv_f32 (P (6))); + + sv_f32_t r2 = svmul_f32_x (pg, r, r); + sv_f32_t y = sv_fma_f32_x (pg, q78, r2, q56); + y = sv_fma_f32_x (pg, y, r2, q34); + y = sv_fma_f32_x (pg, y, r2, q12); + + /* Using p = Log10(2)*n + r*InvLn(10) is slightly faster but less + accurate. */ + sv_f32_t p = sv_fma_n_f32_x (pg, Ln2, n, r); + y = sv_fma_f32_x (pg, y, r2, svmul_n_f32_x (pg, p, InvLn10)); + + if (unlikely (svptest_any (pg, special_cases))) + { + return special_case (x, y, special_cases); + } + return y; +} + +PL_ALIAS (__sv_log10f_x, _ZGVsMxv_log10f) + +PL_SIG (SV, F, 1, log10, 0.01, 11.1) +PL_TEST_ULP (__sv_log10f, 2.82) +PL_TEST_INTERVAL (__sv_log10f, -0.0, -0x1p126, 100) +PL_TEST_INTERVAL (__sv_log10f, 0x1p-149, 0x1p-126, 4000) +PL_TEST_INTERVAL (__sv_log10f, 0x1p-126, 0x1p-23, 50000) +PL_TEST_INTERVAL (__sv_log10f, 0x1p-23, 1.0, 50000) +PL_TEST_INTERVAL (__sv_log10f, 1.0, 100, 50000) +PL_TEST_INTERVAL (__sv_log10f, 100, inf, 50000) +#endif |