| /* ---------------------------------------------------------------------- |
| * Copyright (C) 2010-2014 ARM Limited. All rights reserved. |
| * |
| * $Date: 19. October 2015 |
| * $Revision: V.1.4.5 a |
| * |
| * Project: CMSIS DSP Library |
| * Title: arm_sqrt_q15.c |
| * |
| * Description: Q15 square root function. |
| * |
| * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * - Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * - Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in |
| * the documentation and/or other materials provided with the |
| * distribution. |
| * - Neither the name of ARM LIMITED nor the names of its contributors |
| * may be used to endorse or promote products derived from this |
| * software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, |
| * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; |
| * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER |
| * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN |
| * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| * POSSIBILITY OF SUCH DAMAGE. |
| * -------------------------------------------------------------------- */ |
| #include "arm_math.h" |
| #include "arm_common_tables.h" |
| |
| |
| /** |
| * @ingroup groupFastMath |
| */ |
| |
| /** |
| * @addtogroup SQRT |
| * @{ |
| */ |
| |
| /** |
| * @brief Q15 square root function. |
| * @param[in] in input value. The range of the input value is [0 +1) or 0x0000 to 0x7FFF. |
| * @param[out] *pOut square root of input value. |
| * @return The function returns ARM_MATH_SUCCESS if the input value is positive |
| * and ARM_MATH_ARGUMENT_ERROR if the input is negative. For |
| * negative inputs, the function returns *pOut = 0. |
| */ |
| |
| arm_status arm_sqrt_q15( |
| q15_t in, |
| q15_t * pOut) |
| { |
| q15_t number, temp1, var1, signBits1, half; |
| q31_t bits_val1; |
| float32_t temp_float1; |
| union |
| { |
| q31_t fracval; |
| float32_t floatval; |
| } tempconv; |
| |
| number = in; |
| |
| /* If the input is a positive number then compute the signBits. */ |
| if(number > 0) |
| { |
| signBits1 = __CLZ(number) - 17; |
| |
| /* Shift by the number of signBits1 */ |
| if((signBits1 % 2) == 0) |
| { |
| number = number << signBits1; |
| } |
| else |
| { |
| number = number << (signBits1 - 1); |
| } |
| |
| /* Calculate half value of the number */ |
| half = number >> 1; |
| /* Store the number for later use */ |
| temp1 = number; |
| |
| /* Convert to float */ |
| temp_float1 = number * 3.051757812500000e-005f; |
| /*Store as integer */ |
| tempconv.floatval = temp_float1; |
| bits_val1 = tempconv.fracval; |
| /* Subtract the shifted value from the magic number to give intial guess */ |
| bits_val1 = 0x5f3759df - (bits_val1 >> 1); /* gives initial guess */ |
| /* Store as float */ |
| tempconv.fracval = bits_val1; |
| temp_float1 = tempconv.floatval; |
| /* Convert to integer format */ |
| var1 = (q31_t) (temp_float1 * 16384); |
| |
| /* 1st iteration */ |
| var1 = ((q15_t) ((q31_t) var1 * (0x3000 - |
| ((q15_t) |
| ((((q15_t) |
| (((q31_t) var1 * var1) >> 15)) * |
| (q31_t) half) >> 15))) >> 15)) << 2; |
| /* 2nd iteration */ |
| var1 = ((q15_t) ((q31_t) var1 * (0x3000 - |
| ((q15_t) |
| ((((q15_t) |
| (((q31_t) var1 * var1) >> 15)) * |
| (q31_t) half) >> 15))) >> 15)) << 2; |
| /* 3rd iteration */ |
| var1 = ((q15_t) ((q31_t) var1 * (0x3000 - |
| ((q15_t) |
| ((((q15_t) |
| (((q31_t) var1 * var1) >> 15)) * |
| (q31_t) half) >> 15))) >> 15)) << 2; |
| |
| /* Multiply the inverse square root with the original value */ |
| var1 = ((q15_t) (((q31_t) temp1 * var1) >> 15)) << 1; |
| |
| /* Shift the output down accordingly */ |
| if((signBits1 % 2) == 0) |
| { |
| var1 = var1 >> (signBits1 / 2); |
| } |
| else |
| { |
| var1 = var1 >> ((signBits1 - 1) / 2); |
| } |
| *pOut = var1; |
| |
| return (ARM_MATH_SUCCESS); |
| } |
| /* If the number is a negative number then store zero as its square root value */ |
| else |
| { |
| *pOut = 0; |
| return (ARM_MATH_ARGUMENT_ERROR); |
| } |
| } |
| |
| /** |
| * @} end of SQRT group |
| */ |