diff options
Diffstat (limited to 'pl/math/v_log2f_2u5.c')
-rw-r--r-- | pl/math/v_log2f_2u5.c | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/pl/math/v_log2f_2u5.c b/pl/math/v_log2f_2u5.c new file mode 100644 index 0000000..8f9241b --- /dev/null +++ b/pl/math/v_log2f_2u5.c @@ -0,0 +1,68 @@ +/* + * Single-precision vector log2 function. + * + * Copyright (c) 2022-2023, Arm Limited. + * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception + */ + +#include "v_math.h" +#include "pairwise_hornerf.h" +#include "pl_sig.h" +#include "pl_test.h" +#if V_SUPPORTED + +#define C(i) v_f32 (__v_log2f_data.poly[i]) + +#define Ln2 v_f32 (0x1.62e43p-1f) /* 0x3f317218 */ +#define Min v_u32 (0x00800000) +#define Max v_u32 (0x7f800000) +#define Mask v_u32 (0x007fffff) +#define Off v_u32 (0x3f2aaaab) /* 0.666667 */ + +VPCS_ATTR +NOINLINE static v_f32_t +specialcase (v_f32_t x, v_f32_t y, v_u32_t cmp) +{ + /* Fall back to scalar code. */ + return v_call_f32 (log2f, x, y, cmp); +} + +/* Fast implementation for single precision log2, + relies on same argument reduction as Neon logf. + Maximum error: 2.48 ULPs + __v_log2f(0x1.558174p+0) got 0x1.a9be84p-2 + want 0x1.a9be8p-2. */ +VPCS_ATTR +v_f32_t V_NAME (log2f) (v_f32_t x) +{ + v_u32_t u = v_as_u32_f32 (x); + v_u32_t cmp = v_cond_u32 (u - Min >= Max - Min); + + /* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */ + u -= Off; + v_f32_t n = v_to_f32_s32 (v_as_s32_u32 (u) >> 23); /* signextend. */ + u &= Mask; + u += Off; + v_f32_t r = v_as_f32_u32 (u) - v_f32 (1.0f); + + /* y = log2(1+r) + n. */ + v_f32_t r2 = r * r; + v_f32_t p = PAIRWISE_HORNER_8 (r, r2, C); + v_f32_t y = v_fma_f32 (p, r, n); + + if (unlikely (v_any_u32 (cmp))) + return specialcase (x, y, cmp); + return y; +} +VPCS_ALIAS + +PL_SIG (V, F, 1, log2, 0.01, 11.1) +PL_TEST_ULP (V_NAME (log2f), 1.99) +PL_TEST_EXPECT_FENV_ALWAYS (V_NAME (log2f)) +PL_TEST_INTERVAL (V_NAME (log2f), -0.0, -0x1p126, 100) +PL_TEST_INTERVAL (V_NAME (log2f), 0x1p-149, 0x1p-126, 4000) +PL_TEST_INTERVAL (V_NAME (log2f), 0x1p-126, 0x1p-23, 50000) +PL_TEST_INTERVAL (V_NAME (log2f), 0x1p-23, 1.0, 50000) +PL_TEST_INTERVAL (V_NAME (log2f), 1.0, 100, 50000) +PL_TEST_INTERVAL (V_NAME (log2f), 100, inf, 50000) +#endif |