CMSIS DSP Software Library: arm_sqrt_q31.c Source File

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# arm_sqrt_q31.c

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    00001 /* ----------------------------------------------------------------------
    00002 * Copyright (C) 2010 ARM Limited. All rights reserved.
    00003 *
    00004 * $Date:        15. July 2011
    00005 * $Revision:    V1.0.10
    00006 *
    00007 * Project:      CMSIS DSP Library
    00008 * Title:        arm_sqrt_q31.c
    00009 *
    00010 * Description:  Q31 square root function.
    00011 *
    00012 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
    00013 *
    00014 * Version 1.0.10 2011/7/15
    00015 *    Big Endian support added and Merged M0 and M3/M4 Source code.
    00016 *
    00017 * Version 1.0.2 2010/11/11
    00018 *    Documentation updated.
    00019 *
    00020 * Version 1.0.1 2010/10/05
    00021 *    Production release and review comments incorporated.
    00022 *
    00023 * Version 1.0.0 2010/09/20
    00024 *    Production release and review comments incorporated.
    00025 * -------------------------------------------------------------------- */
    00026
    00027 #include "arm_math.h"
    00028 #include "arm_common_tables.h"
    00029
    00047 arm_status arm_sqrt_q31(
    00048   q31_t in,
    00049   q31_t * pOut)
    00050 {
    00051   q63_t prevOut;
    00052   q31_t oneByOut;
    00053   uint32_t signBits;
    00054
    00055 #ifndef ARM_MATH_CM0
    00056
    00057   /* Run the below code for Cortex-M4 and Cortex-M3 */
    00058
    00059   q63_t out;
    00060
    00061   if(in > 0)
    00062   {
    00063
    00064     /* run for ten iterations */
    00065
    00066     /* Take initial guess as half of the input and first iteration */
    00067     out = (in >> 1) + 0x3FFFFFFF;
    00068
    00069     /* Calculation of reciprocal of out */
    00070     /* oneByOut contains reciprocal of out which is in 2.30 format
    00071        and oneByOut should be upscaled by signBits */
    00072     signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
    00073
    00074     /* 0.5 * (out) */
    00075     out = out >> 1u;
    00076
    00077     /* prevOut = 0.5 * out + (in * (oneByOut << signBits))) */
    00078     prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00079
    00080     /* Third iteration */
    00081     signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
    00082     prevOut = prevOut >> 1u;
    00083     out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00084
    00085     signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
    00086     out = out >> 1u;
    00087     prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00088
    00089     /* Fifth iteration */
    00090     signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
    00091     prevOut = prevOut >> 1u;
    00092     out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00093
    00094     signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
    00095     out = out >> 1u;
    00096     prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00097
    00098     /* Seventh iteration */
    00099     signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
    00100     prevOut = prevOut >> 1u;
    00101     out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00102
    00103     signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
    00104     out = out >> 1u;
    00105     prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00106
    00107     signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
    00108     prevOut = prevOut >> 1u;
    00109     out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00110
    00111     signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
    00112     out = out >> 1u;
    00113     prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00114
    00115     signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
    00116     prevOut = prevOut >> 1u;
    00117     out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00118
    00119     signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
    00120     out = out >> 1u;
    00121     prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00122
    00123     signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
    00124     prevOut = prevOut >> 1u;
    00125     out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00126
    00127     signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
    00128     out = out >> 1u;
    00129     prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00130
    00131     signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
    00132     prevOut = prevOut >> 1u;
    00133     out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00134
    00135     /* tenth iteration */
    00136     signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
    00137     out = out >> 1u;
    00138     *pOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00139
    00140     return (ARM_MATH_SUCCESS);
    00141   }
    00142
    00143 #else
    00144
    00145   /* Run the below code for Cortex-M0 */
    00146
    00147   q63_t out, loopVar;                            /* Temporary variable for output, loop variable */
    00148   if(in > 0)
    00149   {
    00150
    00151     /* run for ten iterations */
    00152
    00153     /* Take initial guess as half of the input and first iteration */
    00154     out = (in >> 1) + 0x3FFFFFFF;
    00155
    00156     /* Calculation of reciprocal of out */
    00157     /* oneByOut contains reciprocal of out which is in 2.30 format
    00158        and oneByOut should be upscaled by sign bits */
    00159     signBits = arm_recip_q31((q31_t) out, &oneByOut, armRecipTableQ31);
    00160
    00161     /* 0.5 * (out) */
    00162     out = out >> 1u;
    00163
    00164     /* prevOut = 0.5 * out + (in * (oneByOut) << signbits) */
    00165     prevOut = out + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00166
    00167
    00168     /* loop for third iteration to tength iteration */
    00169
    00170     for (loopVar = 1; loopVar <= 14; loopVar++)
    00171     {
    00172
    00173       signBits = arm_recip_q31((q31_t) prevOut, &oneByOut, armRecipTableQ31);
    00174       /* 0.5 * (prevOut) */
    00175       prevOut = prevOut >> 1u;
    00176       /* out = 0.5 * prevOut + (in * oneByOut) << signbits))) */
    00177       out = prevOut + (((q31_t) (((q63_t) in * oneByOut) >> 32)) << signBits);
    00178       /* prevOut      = out */
    00179       prevOut = out;
    00180
    00181     }
    00182     /* output is moved to pOut pointer */
    00183     *pOut = prevOut;
    00184
    00185     return (ARM_MATH_SUCCESS);
    00186   }
    00187
    00188 #endif /* #ifndef ARM_MATH_CM0 */
    00189
    00190   else
    00191   {
    00192     *pOut = 0;
    00193     return (ARM_MATH_ARGUMENT_ERROR);
    00194   }
    00195 }
    00196

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