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author | Elliott Hughes <enh@google.com> | 2023-01-26 00:54:27 +0000 |
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committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | 2023-01-26 00:54:27 +0000 |
commit | 3af78e4947651f55c2b28e863782fd8473052cbf (patch) | |
tree | 945eb1832687ad5eb97c433013617dbe107718e5 /pl/math/logf.c | |
parent | 02d5b0cc872a48cd963cf531c958370d14d15280 (diff) | |
parent | 8a481eb48cf7ace04026cbe776d65492f89a6d7d (diff) | |
download | arm-optimized-routines-3af78e4947651f55c2b28e863782fd8473052cbf.tar.gz |
Upgrade ARM-software/optimized-routines to v23.01 am: 62662f115a am: 8783f524be am: 8a481eb48c
Original change: https://android-review.googlesource.com/c/platform/external/arm-optimized-routines/+/2402215
Change-Id: Id535bcfef3f5b328f4666742a1623794a20f982d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
Diffstat (limited to 'pl/math/logf.c')
-rw-r--r-- | pl/math/logf.c | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/pl/math/logf.c b/pl/math/logf.c new file mode 100644 index 0000000..17a74ed --- /dev/null +++ b/pl/math/logf.c @@ -0,0 +1,75 @@ +/* + * Single-precision log function. + * + * Copyright (c) 2017-2023, Arm Limited. + * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception + */ + +#include <math.h> +#include <stdint.h> +#include "math_config.h" + +/* +LOGF_TABLE_BITS = 4 +LOGF_POLY_ORDER = 4 + +ULP error: 0.818 (nearest rounding.) +Relative error: 1.957 * 2^-26 (before rounding.) +*/ + +#define T __logf_data.tab +#define A __logf_data.poly +#define Ln2 __logf_data.ln2 +#define N (1 << LOGF_TABLE_BITS) +#define OFF 0x3f330000 + +float +optr_aor_log_f32 (float x) +{ + /* double_t for better performance on targets with FLT_EVAL_METHOD==2. */ + double_t z, r, r2, y, y0, invc, logc; + uint32_t ix, iz, tmp; + int k, i; + + ix = asuint (x); +#if WANT_ROUNDING + /* Fix sign of zero with downward rounding when x==1. */ + if (unlikely (ix == 0x3f800000)) + return 0; +#endif + if (unlikely (ix - 0x00800000 >= 0x7f800000 - 0x00800000)) + { + /* x < 0x1p-126 or inf or nan. */ + if (ix * 2 == 0) + return __math_divzerof (1); + if (ix == 0x7f800000) /* log(inf) == inf. */ + return x; + if ((ix & 0x80000000) || ix * 2 >= 0xff000000) + return __math_invalidf (x); + /* x is subnormal, normalize it. */ + ix = asuint (x * 0x1p23f); + ix -= 23 << 23; + } + + /* x = 2^k z; where z is in range [OFF,2*OFF] and exact. + The range is split into N subintervals. + The ith subinterval contains z and c is near its center. */ + tmp = ix - OFF; + i = (tmp >> (23 - LOGF_TABLE_BITS)) % N; + k = (int32_t) tmp >> 23; /* arithmetic shift */ + iz = ix - (tmp & 0x1ff << 23); + invc = T[i].invc; + logc = T[i].logc; + z = (double_t) asfloat (iz); + + /* log(x) = log1p(z/c-1) + log(c) + k*Ln2 */ + r = z * invc - 1; + y0 = logc + (double_t) k * Ln2; + + /* Pipelined polynomial evaluation to approximate log1p(r). */ + r2 = r * r; + y = A[1] * r + A[2]; + y = A[0] * r2 + y; + y = y * r2 + (y0 + r); + return eval_as_float (y); +} |