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75 lines
1.8 KiB
75 lines
1.8 KiB
4 months ago
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/*
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* Single-precision vector log function.
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*
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* Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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* See https://llvm.org/LICENSE.txt for license information.
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* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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*/
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#include "mathlib.h"
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#include "v_math.h"
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#if V_SUPPORTED
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static const float Poly[] = {
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/* 3.34 ulp error */
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-0x1.3e737cp-3f, 0x1.5a9aa2p-3f, -0x1.4f9934p-3f, 0x1.961348p-3f,
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-0x1.00187cp-2f, 0x1.555d7cp-2f, -0x1.ffffc8p-2f,
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};
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#define P7 v_f32 (Poly[0])
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#define P6 v_f32 (Poly[1])
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#define P5 v_f32 (Poly[2])
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#define P4 v_f32 (Poly[3])
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#define P3 v_f32 (Poly[4])
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#define P2 v_f32 (Poly[5])
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#define P1 v_f32 (Poly[6])
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#define Ln2 v_f32 (0x1.62e43p-1f) /* 0x3f317218 */
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#define Min v_u32 (0x00800000)
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#define Max v_u32 (0x7f800000)
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#define Mask v_u32 (0x007fffff)
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#define Off v_u32 (0x3f2aaaab) /* 0.666667 */
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VPCS_ATTR
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__attribute__ ((noinline)) static v_f32_t
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specialcase (v_f32_t x, v_f32_t y, v_u32_t cmp)
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{
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/* Fall back to scalar code. */
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return v_call_f32 (logf, x, y, cmp);
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}
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VPCS_ATTR
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v_f32_t
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V_NAME(logf) (v_f32_t x)
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{
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v_f32_t n, p, q, r, r2, y;
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v_u32_t u, cmp;
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u = v_as_u32_f32 (x);
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cmp = v_cond_u32 (u - Min >= Max - Min);
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/* x = 2^n * (1+r), where 2/3 < 1+r < 4/3 */
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u -= Off;
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n = v_to_f32_s32 (v_as_s32_u32 (u) >> 23); /* signextend */
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u &= Mask;
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u += Off;
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r = v_as_f32_u32 (u) - v_f32 (1.0f);
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/* y = log(1+r) + n*ln2. */
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r2 = r * r;
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/* n*ln2 + r + r2*(P1 + r*P2 + r2*(P3 + r*P4 + r2*(P5 + r*P6 + r2*P7))). */
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p = v_fma_f32 (P6, r, P5);
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q = v_fma_f32 (P4, r, P3);
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y = v_fma_f32 (P2, r, P1);
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p = v_fma_f32 (P7, r2, p);
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q = v_fma_f32 (p, r2, q);
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y = v_fma_f32 (q, r2, y);
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p = v_fma_f32 (Ln2, n, r);
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y = v_fma_f32 (y, r2, p);
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if (unlikely (v_any_u32 (cmp)))
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return specialcase (x, y, cmp);
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return y;
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}
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VPCS_ALIAS
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#endif
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