1 /* 2 * Single-precision vector log function. 3 * 4 * Copyright (c) 2019-2023, 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 static const struct data 13 { 14 float poly_0135[4]; 15 float poly_246[3]; 16 float ln2; 17 } data = { 18 .poly_0135 = { 19 /* Coefficients copied from the AdvSIMD routine in math/, then rearranged so 20 that coeffs 0, 1, 3 and 5 can be loaded as a single quad-word, hence used 21 with _lane variant of MLA intrinsic. */ 22 -0x1.3e737cp-3f, 0x1.5a9aa2p-3f, 0x1.961348p-3f, 0x1.555d7cp-2f 23 }, 24 .poly_246 = { -0x1.4f9934p-3f, -0x1.00187cp-2f, -0x1.ffffc8p-2f }, 25 .ln2 = 0x1.62e43p-1f 26 }; 27 28 #define Min (0x00800000) 29 #define Max (0x7f800000) 30 #define Thresh (0x7f000000) /* Max - Min. */ 31 #define Mask (0x007fffff) 32 #define Off (0x3f2aaaab) /* 0.666667. */ 33 34 float optr_aor_log_f32 (float); 35 36 static svfloat32_t NOINLINE 37 special_case (svfloat32_t x, svfloat32_t y, svbool_t cmp) 38 { 39 return sv_call_f32 (optr_aor_log_f32, x, y, cmp); 40 } 41 42 /* Optimised implementation of SVE logf, using the same algorithm and 43 polynomial as the AdvSIMD routine. Maximum error is 3.34 ULPs: 44 SV_NAME_F1 (log)(0x1.557298p+0) got 0x1.26edecp-2 45 want 0x1.26ede6p-2. */ 46 svfloat32_t SV_NAME_F1 (log) (svfloat32_t x, const svbool_t pg) 47 { 48 const struct data *d = ptr_barrier (&data); 49 50 svuint32_t u = svreinterpret_u32 (x); 51 svbool_t cmp = svcmpge (pg, svsub_x (pg, u, Min), Thresh); 52 53 /* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */ 54 u = svsub_x (pg, u, Off); 55 svfloat32_t n = svcvt_f32_x ( 56 pg, svasr_x (pg, svreinterpret_s32 (u), 23)); /* Sign-extend. */ 57 u = svand_x (pg, u, Mask); 58 u = svadd_x (pg, u, Off); 59 svfloat32_t r = svsub_x (pg, svreinterpret_f32 (u), 1.0f); 60 61 /* y = log(1+r) + n*ln2. */ 62 svfloat32_t r2 = svmul_x (pg, r, r); 63 /* n*ln2 + r + r2*(P6 + r*P5 + r2*(P4 + r*P3 + r2*(P2 + r*P1 + r2*P0))). */ 64 svfloat32_t p_0135 = svld1rq (svptrue_b32 (), &d->poly_0135[0]); 65 svfloat32_t p = svmla_lane (sv_f32 (d->poly_246[0]), r, p_0135, 1); 66 svfloat32_t q = svmla_lane (sv_f32 (d->poly_246[1]), r, p_0135, 2); 67 svfloat32_t y = svmla_lane (sv_f32 (d->poly_246[2]), r, p_0135, 3); 68 p = svmla_lane (p, r2, p_0135, 0); 69 70 q = svmla_x (pg, q, r2, p); 71 y = svmla_x (pg, y, r2, q); 72 p = svmla_x (pg, r, n, d->ln2); 73 74 if (unlikely (svptest_any (pg, cmp))) 75 return special_case (x, svmla_x (svnot_z (pg, cmp), p, r2, y), cmp); 76 return svmla_x (pg, p, r2, y); 77 } 78 79 PL_SIG (SV, F, 1, log, 0.01, 11.1) 80 PL_TEST_ULP (SV_NAME_F1 (log), 2.85) 81 PL_TEST_INTERVAL (SV_NAME_F1 (log), -0.0, -inf, 100) 82 PL_TEST_INTERVAL (SV_NAME_F1 (log), 0, 0x1p-126, 100) 83 PL_TEST_INTERVAL (SV_NAME_F1 (log), 0x1p-126, 0x1p-23, 50000) 84 PL_TEST_INTERVAL (SV_NAME_F1 (log), 0x1p-23, 1.0, 50000) 85 PL_TEST_INTERVAL (SV_NAME_F1 (log), 1.0, 100, 50000) 86 PL_TEST_INTERVAL (SV_NAME_F1 (log), 100, inf, 50000) 87