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Diffstat (limited to 'pl/math/sv_log2_3u.c')
| -rw-r--r-- | pl/math/sv_log2_3u.c | 85 |
1 files changed, 85 insertions, 0 deletions
diff --git a/pl/math/sv_log2_3u.c b/pl/math/sv_log2_3u.c new file mode 100644 index 0000000..a0815bb --- /dev/null +++ b/pl/math/sv_log2_3u.c @@ -0,0 +1,85 @@ +/* + * Double-precision SVE log2 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 InvLn2 sv_f64 (0x1.71547652b82fep0) +#define N (1 << V_LOG2_TABLE_BITS) +#define OFF 0x3fe6900900000000 +#define P(i) sv_f64 (__v_log2_data.poly[i]) + +NOINLINE static sv_f64_t +specialcase (sv_f64_t x, sv_f64_t y, const svbool_t cmp) +{ + return sv_call_f64 (log2, x, y, cmp); +} + +/* Double-precision SVE log2 routine. Implements the same algorithm as vector + log10, with coefficients and table entries scaled in extended precision. + The maximum observed error is 2.58 ULP: + __v_log2(0x1.0b556b093869bp+0) got 0x1.fffb34198d9dap-5 + want 0x1.fffb34198d9ddp-5. */ +sv_f64_t +__sv_log2_x (sv_f64_t x, const svbool_t pg) +{ + sv_u64_t ix = sv_as_u64_f64 (x); + sv_u64_t top = svlsr_n_u64_x (pg, ix, 48); + + svbool_t special + = svcmpge_n_u64 (pg, svsub_n_u64_x (pg, top, 0x0010), 0x7ff0 - 0x0010); + + /* x = 2^k z; where z is in range [OFF,2*OFF) and exact. + The range is split into N subintervals. + The ith subinterval contains z and c is near its center. */ + sv_u64_t tmp = svsub_n_u64_x (pg, ix, OFF); + sv_u64_t i + = sv_mod_n_u64_x (pg, svlsr_n_u64_x (pg, tmp, 52 - V_LOG2_TABLE_BITS), N); + sv_f64_t k + = sv_to_f64_s64_x (pg, svasr_n_s64_x (pg, sv_as_s64_u64 (tmp), 52)); + sv_f64_t z = sv_as_f64_u64 ( + svsub_u64_x (pg, ix, svand_n_u64_x (pg, tmp, 0xfffULL << 52))); + + sv_u64_t idx = svmul_n_u64_x (pg, i, 2); + sv_f64_t invc = sv_lookup_f64_x (pg, &__v_log2_data.tab[0].invc, idx); + sv_f64_t log2c = sv_lookup_f64_x (pg, &__v_log2_data.tab[0].log2c, idx); + + /* log2(x) = log1p(z/c-1)/log(2) + log2(c) + k. */ + + sv_f64_t r = sv_fma_f64_x (pg, z, invc, sv_f64 (-1.0)); + sv_f64_t w = sv_fma_f64_x (pg, r, InvLn2, log2c); + + sv_f64_t r2 = svmul_f64_x (pg, r, r); + sv_f64_t p_23 = sv_fma_f64_x (pg, P (3), r, P (2)); + sv_f64_t p_01 = sv_fma_f64_x (pg, P (1), r, P (0)); + sv_f64_t y = sv_fma_f64_x (pg, P (4), r2, p_23); + y = sv_fma_f64_x (pg, y, r2, p_01); + y = sv_fma_f64_x (pg, y, r2, svadd_f64_x (pg, k, w)); + + if (unlikely (svptest_any (pg, special))) + { + return specialcase (x, y, special); + } + return y; +} + +PL_ALIAS (__sv_log2_x, _ZGVsMxv_log2) + +PL_SIG (SV, D, 1, log2, 0.01, 11.1) +PL_TEST_ULP (__sv_log2, 2.09) +PL_TEST_EXPECT_FENV_ALWAYS (__sv_log2) +PL_TEST_INTERVAL (__sv_log2, -0.0, -0x1p126, 1000) +PL_TEST_INTERVAL (__sv_log2, 0.0, 0x1p-126, 4000) +PL_TEST_INTERVAL (__sv_log2, 0x1p-126, 0x1p-23, 50000) +PL_TEST_INTERVAL (__sv_log2, 0x1p-23, 1.0, 50000) +PL_TEST_INTERVAL (__sv_log2, 1.0, 100, 50000) +PL_TEST_INTERVAL (__sv_log2, 100, inf, 50000) + +#endif |