arm_sqrt_q15.c

00001 /* ----------------------------------------------------------------------  
00002 * Copyright (C) 2010 ARM Limited. All rights reserved.  
00003 *  
00004 * $Date:        29. November 2010  
00005 * $Revision:    V1.0.3  
00006 *  
00007 * Project:      CMSIS DSP Library  
00008 * Title:        arm_sqrt_q15.c  
00009 *  
00010 * Description:  Q15 square root function. 
00011 *  
00012 * Target Processor: Cortex-M4/Cortex-M3
00013 *  
00014 * Version 1.0.3 2010/11/29 
00015 *    Re-organized the CMSIS folders and updated documentation.  
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  
00030  
00031 /**  
00032  * @ingroup groupFastMath  
00033  */ 
00034  
00035 /**  
00036  * @addtogroup SQRT  
00037  * @{  
00038  */ 
00039  
00040   /** 
00041    * @brief  Q15 square root function. 
00042    * @param[in]   in     input value.  The range of the input value is [0 +1) or 0x0000 to 0x7FFF. 
00043    * @param[out]  *pOut  square root of input value. 
00044    * @return The function returns ARM_MATH_SUCCESS if input value is positive value or ARM_MATH_ARGUMENT_ERROR if 
00045    * <code>in</code> is negative value and returns zero output for negative values. 
00046    */ 
00047  
00048 arm_status arm_sqrt_q15( 
00049   q15_t in, 
00050   q15_t * pOut) 
00051 { 
00052   q31_t out; 
00053   q31_t prevOut; 
00054   q15_t oneByOut; 
00055   uint32_t sign_bits; 
00056  
00057   if(in > 0) 
00058   { 
00059     /* run for ten iterations */ 
00060  
00061     /* Take initial guess as half of the input and first iteration */ 
00062     out = ((q31_t) in >> 1u) + 0x3FFF; 
00063  
00064     /* Calculation of reciprocal of out */ 
00065     /* oneByOut contains reciprocal of out which is in 2.14 format  
00066        and oneByOut should be upscaled by signBits */ 
00067     sign_bits = arm_recip_q15((q15_t) out, &oneByOut, (q15_t*)armRecipTableQ15); 
00068  
00069     /* 0.5 * (out) */ 
00070     out = out >> 1u; 
00071     /* prevOut = 0.5 * out + (in * (oneByOut << signBits))) */ 
00072     prevOut = out + (((q15_t) (((q31_t) in * oneByOut) >> 16)) << sign_bits); 
00073  
00074     /* Third iteration */ 
00075     sign_bits = arm_recip_q15((q15_t) prevOut, &oneByOut, (q15_t*)armRecipTableQ15); 
00076     prevOut = prevOut >> 1u; 
00077     out = prevOut + (((q15_t) (((q31_t) in * oneByOut) >> 16)) << sign_bits); 
00078  
00079     sign_bits = arm_recip_q15((q15_t) out, &oneByOut, (q15_t*)armRecipTableQ15); 
00080     out = out >> 1u; 
00081     prevOut = out + (((q15_t) (((q31_t) in * oneByOut) >> 16)) << sign_bits); 
00082  
00083     /* Fifth iteration */ 
00084     sign_bits = arm_recip_q15((q15_t) prevOut, &oneByOut, (q15_t*)armRecipTableQ15); 
00085     prevOut = prevOut >> 1u; 
00086     out = prevOut + (((q15_t) (((q31_t) in * oneByOut) >> 16)) << sign_bits); 
00087  
00088     sign_bits = arm_recip_q15((q15_t) out, &oneByOut, (q15_t*)armRecipTableQ15); 
00089     out = out >> 1u; 
00090     prevOut = out + (((q15_t) (((q31_t) in * oneByOut) >> 16)) << sign_bits); 
00091  
00092     /* Seventh iteration */ 
00093     sign_bits = arm_recip_q15((q15_t) prevOut, &oneByOut, (q15_t*)armRecipTableQ15); 
00094     prevOut = prevOut >> 1u; 
00095     out = prevOut + (((q15_t) (((q31_t) in * oneByOut) >> 16)) << sign_bits); 
00096  
00097     sign_bits = arm_recip_q15((q15_t) out, &oneByOut, (q15_t*)armRecipTableQ15); 
00098     out = out >> 1u; 
00099     prevOut = out + (((q15_t) (((q31_t) in * oneByOut) >> 16)) << sign_bits); 
00100  
00101     sign_bits = arm_recip_q15((q15_t) prevOut, &oneByOut, (q15_t*)armRecipTableQ15); 
00102     prevOut = prevOut >> 1u; 
00103     out = prevOut + (((q15_t) (((q31_t) in * oneByOut) >> 16)) << sign_bits); 
00104  
00105     /* tenth iteration */ 
00106     sign_bits = arm_recip_q15((q15_t) out, &oneByOut, (q15_t*)armRecipTableQ15); 
00107     out = out >> 1u; 
00108     *pOut = out + (((q15_t) (((q31_t) in * oneByOut) >> 16)) << sign_bits); 
00109  
00110     return (ARM_MATH_SUCCESS); 
00111   } 
00112   else 
00113   { 
00114  
00115     *pOut = 0; 
00116     return (ARM_MATH_ARGUMENT_ERROR); 
00117   } 
00118  
00119 } 
00120  
00121 /**  
00122  * @} end of SQRT group  
00123  */