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Drivers/CMSIS/DSP/Source/FastMathFunctions/arm_vlog_f16.c

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+/* ----------------------------------------------------------------------
+ * Project:      CMSIS DSP Library
+ * Title:        arm_vlog_f16.c
+ * Description:  Fast vectorized log
+ *
+ * $Date:        23 April 2021
+ * $Revision:    V1.9.0
+ *
+ * Target Processor: Cortex-M and Cortex-A cores
+ * -------------------------------------------------------------------- */
+/*
+ * Copyright (C) 2010-2021 ARM Limited or its affiliates. All rights reserved.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the License); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an AS IS BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "dsp/fast_math_functions_f16.h"
+#include "dsp/support_functions_f16.h"
+
+#if defined(ARM_FLOAT16_SUPPORTED)
+
+/* Degree of the polynomial approximation */
+#define NB_DEG_LOGF16 3
+
+/*
+Related to the Log2 of the number of approximations.
+For instance, with 3 there are 1 + 2^3 polynomials
+*/
+#define NB_DIV_LOGF16 3
+
+/* Length of the LUT table */
+#define NB_LUT_LOGF16 (NB_DEG_LOGF16+1)*(1 + (1<<NB_DIV_LOGF16))
+
+
+/*
+
+LUT of polynomial approximations.
+
+Could be generated with:
+
+ClearAll[lut, coefs, nb, deg];
+nb = 3;
+deg = 3;
+lut = Table[
+   MiniMaxApproximation[
+     Log[x/2^nb + i], {x, {10^-6, 1.0/2^nb}, deg, 0},
+     MaxIterations -> 1000][[2, 1]], {i, 1, 2, (1.0/2^nb)}];
+coefs = Chop@Flatten[CoefficientList[lut, x]];
+
+*/
+static float16_t lut_logf16[NB_LUT_LOGF16]={
+   0,0.125,-0.00781197,0.00063974,0.117783,
+   0.111111,-0.00617212,0.000447935,0.223144,
+   0.1,-0.00499952,0.000327193,0.318454,0.0909091,
+   -0.00413191,0.000246234,0.405465,0.0833333,
+   -0.00347199,0.000189928,0.485508,0.0769231,
+   -0.00295841,0.00014956,0.559616,0.0714286,
+   -0.0025509,0.000119868,0.628609,0.0666667,
+   -0.00222213,0.0000975436,0.693147,
+   0.0625,-0.00195305,0.0000804357};
+
+
+float16_t logf16_scalar(float16_t x)
+{
+    int16_t i =  arm_typecast_s16_f16(x);
+
+    int32_t vecExpUnBiased = (i >> 10) - 15;
+    i = i - (vecExpUnBiased << 10);
+    float16_t vecTmpFlt1 = arm_typecast_f16_s16(i);
+
+    float16_t *lut;
+    int n;
+    float16_t tmp,v;
+
+    tmp = ((_Float16)vecTmpFlt1 - 1.0f16) * (1 << NB_DIV_LOGF16);
+    n = (int)floor((double)tmp);
+    v = (_Float16)tmp - (_Float16)n;
+
+    lut = lut_logf16 + n * (1+NB_DEG_LOGF16);
+
+    float16_t res = lut[NB_DEG_LOGF16-1];
+    for(int j=NB_DEG_LOGF16-2; j >=0 ; j--)
+    {
+       res = (_Float16)lut[j] + (_Float16)v * (_Float16)res;
+    }
+
+    res = (_Float16)res + 0.693147f16 * (_Float16)vecExpUnBiased;
+
+
+    return(res);
+}
+
+#if defined(ARM_MATH_MVE_FLOAT16) && !defined(ARM_MATH_AUTOVECTORIZE)
+
+#include "arm_common_tables.h"
+#include "arm_vec_math_f16.h"
+
+
+float16x8_t vlogq_lut_f16(float16x8_t vecIn)
+{
+    int16x8_t i =  vreinterpretq_s16_f16(vecIn);
+
+    int16x8_t vecExpUnBiased = vsubq_n_s16(vshrq_n_s16(i,10), 15);
+    i = vsubq_s16(i,vshlq_n_s16(vecExpUnBiased,10));
+    float16x8_t vecTmpFlt1 = vreinterpretq_f16_s16(i);
+
+
+    float16x8_t lutV;
+    int16x8_t n;
+    int16x8_t offset;
+
+    float16x8_t tmp,v,res;
+
+    tmp = vmulq_n_f16(vsubq_n_f16(vecTmpFlt1,1.0f16),(_Float16)(1 << NB_DIV_LOGF16));
+
+    n = vcvtq_s16_f16(tmp);
+    v = vsubq_f16(tmp,vcvtq_f16_s16(n));
+
+
+    offset = vmulq_n_s16(n,(1+NB_DEG_LOGF16));
+    offset = vaddq_n_s16(offset,NB_DEG_LOGF16-1);
+
+    res = vldrhq_gather_shifted_offset_f16(lut_logf16,(uint16x8_t)offset);
+    offset = vsubq_n_s16(offset,1);
+
+    for(int j=NB_DEG_LOGF16-2; j >=0 ; j--)
+    {
+       lutV = vldrhq_gather_shifted_offset_f16(lut_logf16,(uint16x8_t)offset);
+       res = vfmaq_f16(lutV,v,res);
+       offset = vsubq_n_s16(offset,1);
+
+    }
+
+    res = vfmaq_n_f16(res,vcvtq_f16_s16(vecExpUnBiased),0.693147f16);
+
+
+    return(res);
+
+}
+
+#endif
+
+/**
+  @ingroup groupFastMath
+ */
+
+/**
+  @addtogroup vlog
+  @{
+ */
+
+/**
+  @brief         Floating-point vector of log values.
+  @param[in]     pSrc       points to the input vector
+  @param[out]    pDst       points to the output vector
+  @param[in]     blockSize  number of samples in each vector
+  @return        none
+ */
+
+
+void arm_vlog_f16(
+  const float16_t * pSrc,
+        float16_t * pDst,
+        uint32_t blockSize)
+{
+   uint32_t blkCnt;
+
+#if defined(ARM_MATH_MVE_FLOAT16) && !defined(ARM_MATH_AUTOVECTORIZE)
+   f16x8_t src;
+   f16x8_t dst;
+
+   blkCnt = blockSize >> 3;
+
+   while (blkCnt > 0U)
+   {
+      src = vld1q(pSrc);
+      dst = vlogq_lut_f16(src);
+      vst1q(pDst, dst);
+
+      pSrc += 8;
+      pDst += 8;
+      /* Decrement loop counter */
+      blkCnt--;
+   }
+
+   blkCnt = blockSize & 7;
+#else
+   blkCnt = blockSize;
+#endif
+
+   while (blkCnt > 0U)
+   {
+      /* C = log(A) */
+
+      /* Calculate log and store result in destination buffer. */
+      *pDst++ = logf16_scalar(*pSrc++);
+
+      /* Decrement loop counter */
+      blkCnt--;
+   }
+}
+
+
+
+/**
+  @} end of vlog group
+ */
+
+
+#endif /* #if defined(ARM_FLOAT16_SUPPORTED) */