80 lines
2.4 KiB
C
80 lines
2.4 KiB
C
/*
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* Single-precision vector/SVE log2 function.
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*
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* Copyright (c) 2022-2023, Arm Limited.
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* SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
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*/
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#include "sv_math.h"
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#include "pl_sig.h"
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#include "pl_test.h"
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#if SV_SUPPORTED
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#define P(i) __v_log2f_data.poly[i]
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#define Ln2 (0x1.62e43p-1f) /* 0x3f317218. */
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#define Min (0x00800000)
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#define Max (0x7f800000)
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#define Mask (0x007fffff)
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#define Off (0x3f2aaaab) /* 0.666667. */
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static NOINLINE sv_f32_t
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specialcase (sv_f32_t x, sv_f32_t y, svbool_t cmp)
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{
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return sv_call_f32 (log2f, x, y, cmp);
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}
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/* Optimised implementation of SVE log2f, using the same algorithm
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and polynomial as Neon log2f. Maximum error is 2.48 ULPs:
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__sv_log2f(0x1.558174p+0) got 0x1.a9be84p-2
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want 0x1.a9be8p-2. */
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sv_f32_t
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__sv_log2f_x (sv_f32_t x, const svbool_t pg)
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{
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sv_u32_t u = sv_as_u32_f32 (x);
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svbool_t special
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= svcmpge_u32 (pg, svsub_n_u32_x (pg, u, Min), sv_u32 (Max - Min));
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/* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */
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u = svsub_n_u32_x (pg, u, Off);
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sv_f32_t n = sv_to_f32_s32_x (pg, svasr_n_s32_x (pg, sv_as_s32_u32 (u),
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23)); /* Sign-extend. */
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u = svand_n_u32_x (pg, u, Mask);
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u = svadd_n_u32_x (pg, u, Off);
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sv_f32_t r = svsub_n_f32_x (pg, sv_as_f32_u32 (u), 1.0f);
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/* y = log2(1+r) + n. */
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sv_f32_t r2 = svmul_f32_x (pg, r, r);
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/* Evaluate polynomial using pairwise Horner scheme. */
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sv_f32_t p67 = sv_fma_n_f32_x (pg, P (7), r, sv_f32 (P (6)));
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sv_f32_t p45 = sv_fma_n_f32_x (pg, P (5), r, sv_f32 (P (4)));
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sv_f32_t p23 = sv_fma_n_f32_x (pg, P (3), r, sv_f32 (P (2)));
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sv_f32_t p01 = sv_fma_n_f32_x (pg, P (1), r, sv_f32 (P (0)));
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sv_f32_t y;
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y = sv_fma_n_f32_x (pg, P (8), r2, p67);
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y = sv_fma_f32_x (pg, y, r2, p45);
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y = sv_fma_f32_x (pg, y, r2, p23);
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y = sv_fma_f32_x (pg, y, r2, p01);
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y = sv_fma_f32_x (pg, y, r, n);
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if (unlikely (svptest_any (pg, special)))
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return specialcase (x, y, special);
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return y;
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}
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PL_ALIAS (__sv_log2f_x, _ZGVsMxv_log2f)
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PL_SIG (SV, F, 1, log2, 0.01, 11.1)
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PL_TEST_ULP (__sv_log2f, 1.99)
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PL_TEST_EXPECT_FENV_ALWAYS (__sv_log2f)
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PL_TEST_INTERVAL (__sv_log2f, -0.0, -0x1p126, 4000)
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PL_TEST_INTERVAL (__sv_log2f, 0.0, 0x1p-126, 4000)
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PL_TEST_INTERVAL (__sv_log2f, 0x1p-126, 0x1p-23, 50000)
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PL_TEST_INTERVAL (__sv_log2f, 0x1p-23, 1.0, 50000)
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PL_TEST_INTERVAL (__sv_log2f, 1.0, 100, 50000)
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PL_TEST_INTERVAL (__sv_log2f, 100, inf, 50000)
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#endif // SV_SUPPORTED
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