92 lines
3.1 KiB
C
Executable File
92 lines
3.1 KiB
C
Executable File
/*------------------------------------------------------------------------------
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Copyright 2016 Sony Semiconductor Solutions Corporation
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Last Updated : 2016/06/24
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Modification ID : 3b74e280b7ad8ce430b6a9419ac53e8f2e3737f9
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------------------------------------------------------------------------------*/
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/*------------------------------------------------------------------------------
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Includes
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------------------------------------------------------------------------------*/
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#include "sony_math.h"
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/*------------------------------------------------------------------------------
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Defines
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------------------------------------------------------------------------------*/
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#define MAX_BIT_PRECISION 5
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#define FRAC_BITMASK 0x1F /**< Depends upon MAX_BIT_PRECISION. */
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#define LOG2_10_100X 332 /**< log2 (10) */
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#define LOG2_E_100X 144 /**< log2 (e) */
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/*------------------------------------------------------------------------------
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Statics
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------------------------------------------------------------------------------*/
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/**
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@brief Look up table for decimal portion of log2 calculation.
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*/
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static const uint8_t log2LookUp[] = {
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0, /* 0 */ 4, /* 0.04439 */
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9, /* 0.08746 */ 13, /* 0.12928 */
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17, /* 0.16993 */ 21, /* 0.20945 */
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25, /* 0.24793 */ 29, /* 0.28540 */
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32, /* 0.32193 */ 36, /* 0.35755 */
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39, /* 0.39232 */ 43, /* 0.42627 */
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46, /* 0.45943 */ 49, /* 0.49185 */
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52, /* 0.52356 */ 55, /* 0.55249 */
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58, /* 0.58496 */ 61, /* 0.61471 */
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64, /* 0.64386 */ 67, /* 0.67246 */
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70, /* 0.70044 */ 73, /* 0.72792 */
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75, /* 0.75489 */ 78, /* 0.78136 */
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81, /* 0.80736 */ 83, /* 0.83289 */
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86, /* 0.85798 */ 88, /* 0.88264 */
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91, /* 0.90689 */ 93, /* 0.93074 */
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95, /* 0.95420 */ 98 /* 0.97728 */
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};
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/*------------------------------------------------------------------------------
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Functions
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------------------------------------------------------------------------------*/
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uint32_t sony_math_log2 (uint32_t x)
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{
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uint8_t count = 0;
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uint8_t index = 0;
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uint32_t xval = x;
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/* Get the MSB position. */
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for (x >>= 1; x > 0; x >>= 1) {
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count++;
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}
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x = count * 100;
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if (count > 0) {
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if (count <= MAX_BIT_PRECISION) {
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/* Mask the bottom bits. */
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index = (uint8_t) (xval << (MAX_BIT_PRECISION - count)) & FRAC_BITMASK;
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x += log2LookUp[index];
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}
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else {
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/* Mask the bits just below the radix. */
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index = (uint8_t) (xval >> (count - MAX_BIT_PRECISION)) & FRAC_BITMASK;
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x += log2LookUp[index];
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}
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}
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return (x);
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}
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uint32_t sony_math_log10 (uint32_t x)
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{
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/* log10(x) = log2 (x) / log2 (10) */
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/* Note uses: logN (x) = logM (x) / logM (N) */
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return ((100 * sony_math_log2 (x) + LOG2_10_100X / 2) / LOG2_10_100X);
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}
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uint32_t sony_math_log (uint32_t x)
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{
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/* ln (x) = log2 (x) / log2(e) */
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return ((100 * sony_math_log2 (x) + LOG2_E_100X / 2) / LOG2_E_100X);
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}
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