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CMSIS DSP Lib

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cmsis_dsp/FastMathFunctions/arm_sqrt_q15.c@1:fdd22bb7aa52, 2012-11-28 (annotated)

Committer:
emilmont
Date:
Wed Nov 28 12:30:09 2012 +0000
Revision:
1:fdd22bb7aa52
Child:
2:da51fb522205
DSP library code

Who changed what in which revision?

UserRevisionLine numberNew contents of line
emilmont 1:fdd22bb7aa52 1 /* ----------------------------------------------------------------------
emilmont 1:fdd22bb7aa52 2 * Copyright (C) 2011 ARM Limited. All rights reserved.
emilmont 1:fdd22bb7aa52 3 *
emilmont 1:fdd22bb7aa52 4 * $Date: 15. February 2012
emilmont 1:fdd22bb7aa52 5 * $Revision: V1.1.0
emilmont 1:fdd22bb7aa52 6 *
emilmont 1:fdd22bb7aa52 7 * Project: CMSIS DSP Library
emilmont 1:fdd22bb7aa52 8 * Title: arm_sqrt_q15.c
emilmont 1:fdd22bb7aa52 9 *
emilmont 1:fdd22bb7aa52 10 * Description: Q15 square root function.
emilmont 1:fdd22bb7aa52 11 *
emilmont 1:fdd22bb7aa52 12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
emilmont 1:fdd22bb7aa52 13 *
emilmont 1:fdd22bb7aa52 14 * Version 1.1.0 2012/02/15
emilmont 1:fdd22bb7aa52 15 * Updated with more optimizations, bug fixes and minor API changes.
emilmont 1:fdd22bb7aa52 16 *
emilmont 1:fdd22bb7aa52 17 * Version 1.0.0 2011/03/08
emilmont 1:fdd22bb7aa52 18 * Alpha release.
emilmont 1:fdd22bb7aa52 19 *
emilmont 1:fdd22bb7aa52 20 * Version 1.0.1 2011/09/30
emilmont 1:fdd22bb7aa52 21 * Beta release.
emilmont 1:fdd22bb7aa52 22 *
emilmont 1:fdd22bb7aa52 23 * -------------------------------------------------------------------- */
emilmont 1:fdd22bb7aa52 24 #include "arm_math.h"
emilmont 1:fdd22bb7aa52 25 #include "arm_common_tables.h"
emilmont 1:fdd22bb7aa52 26
emilmont 1:fdd22bb7aa52 27
emilmont 1:fdd22bb7aa52 28 /**
emilmont 1:fdd22bb7aa52 29 * @ingroup groupFastMath
emilmont 1:fdd22bb7aa52 30 */
emilmont 1:fdd22bb7aa52 31
emilmont 1:fdd22bb7aa52 32 /**
emilmont 1:fdd22bb7aa52 33 * @addtogroup SQRT
emilmont 1:fdd22bb7aa52 34 * @{
emilmont 1:fdd22bb7aa52 35 */
emilmont 1:fdd22bb7aa52 36
emilmont 1:fdd22bb7aa52 37 /**
emilmont 1:fdd22bb7aa52 38 * @brief Q15 square root function.
emilmont 1:fdd22bb7aa52 39 * @param[in] in input value. The range of the input value is [0 +1) or 0x0000 to 0x7FFF.
emilmont 1:fdd22bb7aa52 40 * @param[out] *pOut square root of input value.
emilmont 1:fdd22bb7aa52 41 * @return The function returns ARM_MATH_SUCCESS if input value is positive value or ARM_MATH_ARGUMENT_ERROR if
emilmont 1:fdd22bb7aa52 42 * <code>in</code> is negative value and returns zero output for negative values.
emilmont 1:fdd22bb7aa52 43 */
emilmont 1:fdd22bb7aa52 44
emilmont 1:fdd22bb7aa52 45 arm_status arm_sqrt_q15(
emilmont 1:fdd22bb7aa52 46 q15_t in,
emilmont 1:fdd22bb7aa52 47 q15_t * pOut)
emilmont 1:fdd22bb7aa52 48 {
emilmont 1:fdd22bb7aa52 49 q15_t number, temp1, var1, signBits1, half;
emilmont 1:fdd22bb7aa52 50 q31_t bits_val1;
emilmont 1:fdd22bb7aa52 51 float32_t temp_float1;
emilmont 1:fdd22bb7aa52 52
emilmont 1:fdd22bb7aa52 53 number = in;
emilmont 1:fdd22bb7aa52 54
emilmont 1:fdd22bb7aa52 55 /* If the input is a positive number then compute the signBits. */
emilmont 1:fdd22bb7aa52 56 if(number > 0)
emilmont 1:fdd22bb7aa52 57 {
emilmont 1:fdd22bb7aa52 58 signBits1 = __CLZ(number) - 17;
emilmont 1:fdd22bb7aa52 59
emilmont 1:fdd22bb7aa52 60 /* Shift by the number of signBits1 */
emilmont 1:fdd22bb7aa52 61 if((signBits1 % 2) == 0)
emilmont 1:fdd22bb7aa52 62 {
emilmont 1:fdd22bb7aa52 63 number = number << signBits1;
emilmont 1:fdd22bb7aa52 64 }
emilmont 1:fdd22bb7aa52 65 else
emilmont 1:fdd22bb7aa52 66 {
emilmont 1:fdd22bb7aa52 67 number = number << (signBits1 - 1);
emilmont 1:fdd22bb7aa52 68 }
emilmont 1:fdd22bb7aa52 69
emilmont 1:fdd22bb7aa52 70 /* Calculate half value of the number */
emilmont 1:fdd22bb7aa52 71 half = number >> 1;
emilmont 1:fdd22bb7aa52 72 /* Store the number for later use */
emilmont 1:fdd22bb7aa52 73 temp1 = number;
emilmont 1:fdd22bb7aa52 74
emilmont 1:fdd22bb7aa52 75 /*Convert to float */
emilmont 1:fdd22bb7aa52 76 temp_float1 = number * 3.051757812500000e-005f;
emilmont 1:fdd22bb7aa52 77 /*Store as integer */
emilmont 1:fdd22bb7aa52 78 bits_val1 = *(int *) &temp_float1;
emilmont 1:fdd22bb7aa52 79 /* Subtract the shifted value from the magic number to give intial guess */
emilmont 1:fdd22bb7aa52 80 bits_val1 = 0x5f3759df - (bits_val1 >> 1); // gives initial guess
emilmont 1:fdd22bb7aa52 81 /* Store as float */
emilmont 1:fdd22bb7aa52 82 temp_float1 = *(float *) &bits_val1;
emilmont 1:fdd22bb7aa52 83 /* Convert to integer format */
emilmont 1:fdd22bb7aa52 84 var1 = (q31_t) (temp_float1 * 16384);
emilmont 1:fdd22bb7aa52 85
emilmont 1:fdd22bb7aa52 86 /* 1st iteration */
emilmont 1:fdd22bb7aa52 87 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
emilmont 1:fdd22bb7aa52 88 ((q15_t)
emilmont 1:fdd22bb7aa52 89 ((((q15_t)
emilmont 1:fdd22bb7aa52 90 (((q31_t) var1 * var1) >> 15)) *
emilmont 1:fdd22bb7aa52 91 (q31_t) half) >> 15))) >> 15)) << 2;
emilmont 1:fdd22bb7aa52 92 /* 2nd iteration */
emilmont 1:fdd22bb7aa52 93 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
emilmont 1:fdd22bb7aa52 94 ((q15_t)
emilmont 1:fdd22bb7aa52 95 ((((q15_t)
emilmont 1:fdd22bb7aa52 96 (((q31_t) var1 * var1) >> 15)) *
emilmont 1:fdd22bb7aa52 97 (q31_t) half) >> 15))) >> 15)) << 2;
emilmont 1:fdd22bb7aa52 98 /* 3rd iteration */
emilmont 1:fdd22bb7aa52 99 var1 = ((q15_t) ((q31_t) var1 * (0x3000 -
emilmont 1:fdd22bb7aa52 100 ((q15_t)
emilmont 1:fdd22bb7aa52 101 ((((q15_t)
emilmont 1:fdd22bb7aa52 102 (((q31_t) var1 * var1) >> 15)) *
emilmont 1:fdd22bb7aa52 103 (q31_t) half) >> 15))) >> 15)) << 2;
emilmont 1:fdd22bb7aa52 104
emilmont 1:fdd22bb7aa52 105 /* Multiply the inverse square root with the original value */
emilmont 1:fdd22bb7aa52 106 var1 = ((q15_t) (((q31_t) temp1 * var1) >> 15)) << 1;
emilmont 1:fdd22bb7aa52 107
emilmont 1:fdd22bb7aa52 108 /* Shift the output down accordingly */
emilmont 1:fdd22bb7aa52 109 if((signBits1 % 2) == 0)
emilmont 1:fdd22bb7aa52 110 {
emilmont 1:fdd22bb7aa52 111 var1 = var1 >> (signBits1 / 2);
emilmont 1:fdd22bb7aa52 112 }
emilmont 1:fdd22bb7aa52 113 else
emilmont 1:fdd22bb7aa52 114 {
emilmont 1:fdd22bb7aa52 115 var1 = var1 >> ((signBits1 - 1) / 2);
emilmont 1:fdd22bb7aa52 116 }
emilmont 1:fdd22bb7aa52 117 *pOut = var1;
emilmont 1:fdd22bb7aa52 118
emilmont 1:fdd22bb7aa52 119 return (ARM_MATH_SUCCESS);
emilmont 1:fdd22bb7aa52 120 }
emilmont 1:fdd22bb7aa52 121 /* If the number is a negative number then store zero as its square root value */
emilmont 1:fdd22bb7aa52 122 else
emilmont 1:fdd22bb7aa52 123 {
emilmont 1:fdd22bb7aa52 124 *pOut = 0;
emilmont 1:fdd22bb7aa52 125 return (ARM_MATH_ARGUMENT_ERROR);
emilmont 1:fdd22bb7aa52 126 }
emilmont 1:fdd22bb7aa52 127 }
emilmont 1:fdd22bb7aa52 128
emilmont 1:fdd22bb7aa52 129 /**
emilmont 1:fdd22bb7aa52 130 * @} end of SQRT group
emilmont 1:fdd22bb7aa52 131 */