mirror of https://github.com/ARMmbed/mbed-os.git
132 lines
3.7 KiB
C
132 lines
3.7 KiB
C
/* ----------------------------------------------------------------------
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* Copyright (C) 2011 ARM Limited. All rights reserved.
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*
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* $Date: 15. February 2012
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* $Revision: V1.1.0
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*
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* Project: CMSIS DSP Library
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* Title: arm_sqrt_q15.c
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*
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* Description: Q15 square root function.
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*
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* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
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*
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* Version 1.1.0 2012/02/15
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* Updated with more optimizations, bug fixes and minor API changes.
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*
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* Version 1.0.0 2011/03/08
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* Alpha release.
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*
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* Version 1.0.1 2011/09/30
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* Beta release.
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*
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* -------------------------------------------------------------------- */
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#include "arm_math.h"
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#include "arm_common_tables.h"
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/**
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* @ingroup groupFastMath
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*/
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/**
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* @addtogroup SQRT
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* @{
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*/
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/**
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* @brief Q15 square root function.
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* @param[in] in input value. The range of the input value is [0 +1) or 0x0000 to 0x7FFF.
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* @param[out] *pOut square root of input value.
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* @return The function returns ARM_MATH_SUCCESS if input value is positive value or ARM_MATH_ARGUMENT_ERROR if
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* <code>in</code> is negative value and returns zero output for negative values.
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*/
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arm_status arm_sqrt_q15(
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q15_t in,
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q15_t * pOut)
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{
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q15_t number, temp1, var1, signBits1, half;
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q31_t bits_val1;
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float32_t temp_float1;
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number = in;
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/* If the input is a positive number then compute the signBits. */
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if(number > 0)
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{
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signBits1 = __CLZ(number) - 17;
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/* Shift by the number of signBits1 */
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if((signBits1 % 2) == 0)
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{
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number = number << signBits1;
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}
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else
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{
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number = number << (signBits1 - 1);
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}
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/* Calculate half value of the number */
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half = number >> 1;
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/* Store the number for later use */
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temp1 = number;
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/*Convert to float */
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temp_float1 = number * 3.051757812500000e-005f;
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/*Store as integer */
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bits_val1 = *(int *) &temp_float1;
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/* Subtract the shifted value from the magic number to give intial guess */
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bits_val1 = 0x5f3759df - (bits_val1 >> 1); // gives initial guess
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/* Store as float */
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temp_float1 = *(float *) &bits_val1;
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/* Convert to integer format */
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var1 = (q31_t) (temp_float1 * 16384);
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/* 1st iteration */
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var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
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((q15_t)
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((((q15_t)
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(((q31_t) var1 * var1) >> 15)) *
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(q31_t) half) >> 15))) >> 15)) << 2;
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/* 2nd iteration */
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var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
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((q15_t)
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((((q15_t)
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(((q31_t) var1 * var1) >> 15)) *
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(q31_t) half) >> 15))) >> 15)) << 2;
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/* 3rd iteration */
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var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
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((q15_t)
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((((q15_t)
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(((q31_t) var1 * var1) >> 15)) *
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(q31_t) half) >> 15))) >> 15)) << 2;
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/* Multiply the inverse square root with the original value */
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var1 = ((q15_t) (((q31_t) temp1 * var1) >> 15)) << 1;
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/* Shift the output down accordingly */
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if((signBits1 % 2) == 0)
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{
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var1 = var1 >> (signBits1 / 2);
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}
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else
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{
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var1 = var1 >> ((signBits1 - 1) / 2);
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}
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*pOut = var1;
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return (ARM_MATH_SUCCESS);
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}
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/* If the number is a negative number then store zero as its square root value */
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else
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{
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*pOut = 0;
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return (ARM_MATH_ARGUMENT_ERROR);
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}
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}
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/**
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* @} end of SQRT group
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*/
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