/github/workspace/src/FastMathFunctions/kernels/plp_sqrt_q16s_rv32im.c

Functions

	Name
void	plp_sqrt_q16s_rv32im(const int16_t restrict pSrc, const uint32_t fracBits, int16_t restrict pRes) Square root of a 16-bit fixed point number for RV32IM extension.

Defines

	Name
	sqrt2

Functions Documentation

function plp_sqrt_q16s_rv32im

void plp_sqrt_q16s_rv32im(
    const int16_t *__restrict__ pSrc,
    const uint32_t fracBits,
    int16_t *__restrict__ pRes
)

Square root of a 16-bit fixed point number for RV32IM extension.

Parameters:

• pSrc points to the input vector
• pRes Square root returned here

Return: none

Square root of a 16-bit fixed point number for XPULPV2 extension.

Macros Documentation

define sqrt2

#define sqrt2 0b1011010100000100

Source code

/* =====================================================================
 * Project:      PULP DSP Library
 * Title:        plp_sqrt_q16s_rv32im.c
 * Description:  16-Bit fixed point square root kernel
 *
 * $Date:        02.07.2020
 *
 * Target Processor: PULP cores
 * ===================================================================== */
/*
 * Copyright (C) 2020 ETH Zurich and University of Bologna.
 *
 * Author: Moritz Scherer, ETH Zurich
 *
 * 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.

 *
 * Notice: project inspired by ARM CMSIS DSP and parts of source code
 * ported and adopted for RISC-V PULP platform from ARM CMSIS DSP
 * released under Copyright (C) 2010-2019 ARM Limited or its affiliates
 * with Apache-2.0.
 */

#define sqrt2 0b1011010100000100
#include "plp_math.h"

void plp_sqrt_q16s_rv32im(const int16_t *__restrict__ pSrc,
                          const uint32_t fracBits,
                          int16_t *__restrict__ pRes) {

    int16_t number, temp1, intermediate_fixpoint, signBits, half;

    number = *pSrc;

    /* If the input is a positive number then compute the signBits. */
    if (number > 0) {
        signBits = __builtin_clz(number) - 17;

        /* Shift by the number of signBits */
        if ((signBits % 2) == 0) {
            number = number << signBits;
        } else {
            number = number << (signBits - 1);
        }

        /* Calculate half value of the number */
        half = number >> 1;
        /* Store the number for later use */
        temp1 = number;
        /* Initial guess for 1/(2sqrt(x)) */
        intermediate_fixpoint = (sqrt2 >> 1) - (((sqrt2 >> 1) * (temp1 - 0x40000000)) >>
                                                15); // Taylor at 0.5: sqrt(2)/2 - sqrt(2)/2*(x-0.5)

        for (int i = 0; i < 12; i++) {

            intermediate_fixpoint =
                ((int16_t)((int32_t)intermediate_fixpoint *
                               (0x3000 - ((int16_t)((((int16_t)(((int32_t)intermediate_fixpoint *
                                                                 intermediate_fixpoint) >>
                                                                15)) *
                                                     (int32_t)half) >>
                                                    15))) >>
                           15))
                << 2;
        }

        intermediate_fixpoint = ((int16_t)(((int32_t)temp1 * intermediate_fixpoint) >> 15)) << 1;

        if ((16 - fracBits) > 1) {
            intermediate_fixpoint = intermediate_fixpoint >> ((int32_t)((16 - fracBits)) >> 1);
            if ((16 - fracBits) % 2 == 0) {
                intermediate_fixpoint = ((int32_t)intermediate_fixpoint * sqrt2) >> 15;
            }
        }

        if ((signBits % 2) == 0) {
            intermediate_fixpoint = intermediate_fixpoint >> (signBits / 2);
        } else {
            intermediate_fixpoint = intermediate_fixpoint >> ((signBits - 1) / 2);
        }
        *pRes = intermediate_fixpoint;

    } else {
        *pRes = 0;
    }
}

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Updated on 2023-03-01 at 16:16:32 +0000