1 /* 2 * Single-precision vector/SVE log2 function. 3 * 4 * Copyright (c) 2022-2023, Arm Limited. 5 * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception 6 */ 7 8 #include "sv_math.h" 9 #include "pl_sig.h" 10 #include "pl_test.h" 11 12 #if SV_SUPPORTED 13 14 #define P(i) __v_log2f_data.poly[i] 15 16 #define Ln2 (0x1.62e43p-1f) /* 0x3f317218. */ 17 #define Min (0x00800000) 18 #define Max (0x7f800000) 19 #define Mask (0x007fffff) 20 #define Off (0x3f2aaaab) /* 0.666667. */ 21 22 static NOINLINE sv_f32_t 23 specialcase (sv_f32_t x, sv_f32_t y, svbool_t cmp) 24 { 25 return sv_call_f32 (log2f, x, y, cmp); 26 } 27 28 /* Optimised implementation of SVE log2f, using the same algorithm 29 and polynomial as Neon log2f. Maximum error is 2.48 ULPs: 30 __sv_log2f(0x1.558174p+0) got 0x1.a9be84p-2 31 want 0x1.a9be8p-2. */ 32 sv_f32_t 33 __sv_log2f_x (sv_f32_t x, const svbool_t pg) 34 { 35 sv_u32_t u = sv_as_u32_f32 (x); 36 svbool_t special 37 = svcmpge_u32 (pg, svsub_n_u32_x (pg, u, Min), sv_u32 (Max - Min)); 38 39 /* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */ 40 u = svsub_n_u32_x (pg, u, Off); 41 sv_f32_t n = sv_to_f32_s32_x (pg, svasr_n_s32_x (pg, sv_as_s32_u32 (u), 42 23)); /* Sign-extend. */ 43 u = svand_n_u32_x (pg, u, Mask); 44 u = svadd_n_u32_x (pg, u, Off); 45 sv_f32_t r = svsub_n_f32_x (pg, sv_as_f32_u32 (u), 1.0f); 46 47 /* y = log2(1+r) + n. */ 48 sv_f32_t r2 = svmul_f32_x (pg, r, r); 49 50 /* Evaluate polynomial using pairwise Horner scheme. */ 51 sv_f32_t p67 = sv_fma_n_f32_x (pg, P (7), r, sv_f32 (P (6))); 52 sv_f32_t p45 = sv_fma_n_f32_x (pg, P (5), r, sv_f32 (P (4))); 53 sv_f32_t p23 = sv_fma_n_f32_x (pg, P (3), r, sv_f32 (P (2))); 54 sv_f32_t p01 = sv_fma_n_f32_x (pg, P (1), r, sv_f32 (P (0))); 55 sv_f32_t y; 56 y = sv_fma_n_f32_x (pg, P (8), r2, p67); 57 y = sv_fma_f32_x (pg, y, r2, p45); 58 y = sv_fma_f32_x (pg, y, r2, p23); 59 y = sv_fma_f32_x (pg, y, r2, p01); 60 y = sv_fma_f32_x (pg, y, r, n); 61 62 if (unlikely (svptest_any (pg, special))) 63 return specialcase (x, y, special); 64 return y; 65 } 66 67 PL_ALIAS (__sv_log2f_x, _ZGVsMxv_log2f) 68 69 PL_SIG (SV, F, 1, log2, 0.01, 11.1) 70 PL_TEST_ULP (__sv_log2f, 1.99) 71 PL_TEST_EXPECT_FENV_ALWAYS (__sv_log2f) 72 PL_TEST_INTERVAL (__sv_log2f, -0.0, -0x1p126, 4000) 73 PL_TEST_INTERVAL (__sv_log2f, 0.0, 0x1p-126, 4000) 74 PL_TEST_INTERVAL (__sv_log2f, 0x1p-126, 0x1p-23, 50000) 75 PL_TEST_INTERVAL (__sv_log2f, 0x1p-23, 1.0, 50000) 76 PL_TEST_INTERVAL (__sv_log2f, 1.0, 100, 50000) 77 PL_TEST_INTERVAL (__sv_log2f, 100, inf, 50000) 78 79 #endif // SV_SUPPORTED 80