arm_sqrt_q31.c 5.1 KB

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  1. /* ----------------------------------------------------------------------
  2. * Copyright (C) 2010-2014 ARM Limited. All rights reserved.
  3. *
  4. * $Date: 12. March 2014
  5. * $Revision: V1.4.4
  6. *
  7. * Project: CMSIS DSP Library
  8. * Title: arm_sqrt_q31.c
  9. *
  10. * Description: Q31 square root function.
  11. *
  12. * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
  13. *
  14. * Redistribution and use in source and binary forms, with or without
  15. * modification, are permitted provided that the following conditions
  16. * are met:
  17. * - Redistributions of source code must retain the above copyright
  18. * notice, this list of conditions and the following disclaimer.
  19. * - Redistributions in binary form must reproduce the above copyright
  20. * notice, this list of conditions and the following disclaimer in
  21. * the documentation and/or other materials provided with the
  22. * distribution.
  23. * - Neither the name of ARM LIMITED nor the names of its contributors
  24. * may be used to endorse or promote products derived from this
  25. * software without specific prior written permission.
  26. *
  27. * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  28. * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  29. * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  30. * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  31. * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  32. * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  33. * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  34. * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  35. * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  36. * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  37. * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  38. * POSSIBILITY OF SUCH DAMAGE.
  39. * -------------------------------------------------------------------- */
  40. #include "arm_math.h"
  41. #include "arm_common_tables.h"
  42. /**
  43. * @ingroup groupFastMath
  44. */
  45. /**
  46. * @addtogroup SQRT
  47. * @{
  48. */
  49. /**
  50. * @brief Q31 square root function.
  51. * @param[in] in input value. The range of the input value is [0 +1) or 0x00000000 to 0x7FFFFFFF.
  52. * @param[out] *pOut square root of input value.
  53. * @return The function returns ARM_MATH_SUCCESS if the input value is positive
  54. * and ARM_MATH_ARGUMENT_ERROR if the input is negative. For
  55. * negative inputs, the function returns *pOut = 0.
  56. */
  57. arm_status arm_sqrt_q31(
  58. q31_t in,
  59. q31_t * pOut)
  60. {
  61. q31_t number, temp1, bits_val1, var1, signBits1, half;
  62. float32_t temp_float1;
  63. union
  64. {
  65. q31_t fracval;
  66. float32_t floatval;
  67. } tempconv;
  68. number = in;
  69. /* If the input is a positive number then compute the signBits. */
  70. if(number > 0)
  71. {
  72. signBits1 = __CLZ(number) - 1;
  73. /* Shift by the number of signBits1 */
  74. if((signBits1 % 2) == 0)
  75. {
  76. number = number << signBits1;
  77. }
  78. else
  79. {
  80. number = number << (signBits1 - 1);
  81. }
  82. /* Calculate half value of the number */
  83. half = number >> 1;
  84. /* Store the number for later use */
  85. temp1 = number;
  86. /*Convert to float */
  87. temp_float1 = number * 4.6566128731e-010f;
  88. /*Store as integer */
  89. tempconv.floatval = temp_float1;
  90. bits_val1 = tempconv.fracval;
  91. /* Subtract the shifted value from the magic number to give intial guess */
  92. bits_val1 = 0x5f3759df - (bits_val1 >> 1); // gives initial guess
  93. /* Store as float */
  94. tempconv.fracval = bits_val1;
  95. temp_float1 = tempconv.floatval;
  96. /* Convert to integer format */
  97. var1 = (q31_t) (temp_float1 * 1073741824);
  98. /* 1st iteration */
  99. var1 = ((q31_t) ((q63_t) var1 * (0x30000000 -
  100. ((q31_t)
  101. ((((q31_t)
  102. (((q63_t) var1 * var1) >> 31)) *
  103. (q63_t) half) >> 31))) >> 31)) << 2;
  104. /* 2nd iteration */
  105. var1 = ((q31_t) ((q63_t) var1 * (0x30000000 -
  106. ((q31_t)
  107. ((((q31_t)
  108. (((q63_t) var1 * var1) >> 31)) *
  109. (q63_t) half) >> 31))) >> 31)) << 2;
  110. /* 3rd iteration */
  111. var1 = ((q31_t) ((q63_t) var1 * (0x30000000 -
  112. ((q31_t)
  113. ((((q31_t)
  114. (((q63_t) var1 * var1) >> 31)) *
  115. (q63_t) half) >> 31))) >> 31)) << 2;
  116. /* Multiply the inverse square root with the original value */
  117. var1 = ((q31_t) (((q63_t) temp1 * var1) >> 31)) << 1;
  118. /* Shift the output down accordingly */
  119. if((signBits1 % 2) == 0)
  120. {
  121. var1 = var1 >> (signBits1 / 2);
  122. }
  123. else
  124. {
  125. var1 = var1 >> ((signBits1 - 1) / 2);
  126. }
  127. *pOut = var1;
  128. return (ARM_MATH_SUCCESS);
  129. }
  130. /* If the number is a negative number then store zero as its square root value */
  131. else
  132. {
  133. *pOut = 0;
  134. return (ARM_MATH_ARGUMENT_ERROR);
  135. }
  136. }
  137. /**
  138. * @} end of SQRT group
  139. */