432e2ecc13
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@22298 a1c6a512-1295-4272-9138-f99709370657
66 lines
1.4 KiB
C
66 lines
1.4 KiB
C
#include "fixp_math.h"
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inline int32_t fixmul31(int32_t x, int32_t y)
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{
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int64_t temp;
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temp = x;
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temp *= y;
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temp >>= 31; //16+31-16 = 31 bits
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return (int32_t)temp;
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}
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/*
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* Fast integer square root adapted from algorithm,
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* Martin Guy @ UKC, June 1985.
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* Originally from a book on programming abaci by Mr C. Woo.
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* This is taken from :
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* http://wiki.forum.nokia.com/index.php/How_to_use_fixed_point_maths#How_to_get_square_root_for_integers
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* with a added shift up of the result by 8 bits to return result in 16.16 fixed-point representation.
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*/
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inline int32_t fastSqrt(int32_t n)
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{
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/*
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* Logically, these are unsigned.
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* We need the sign bit to test
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* whether (op - res - one) underflowed.
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*/
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int32_t op, res, one;
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op = n;
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res = 0;
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/* "one" starts at the highest power of four <= than the argument. */
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one = 1 << 30; /* second-to-top bit set */
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while (one > op) one >>= 2;
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while (one != 0)
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{
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if (op >= res + one)
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{
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op = op - (res + one);
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res = res + (one<<1);
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}
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res >>= 1;
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one >>= 2;
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}
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return(res << 8);
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}
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inline int32_t fixmul16(int32_t x, int32_t y)
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{
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int64_t temp;
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temp = x;
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temp *= y;
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temp >>= 16;
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return (int32_t)temp;
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}
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inline int32_t fixdiv16(int32_t x, int32_t y)
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{
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int64_t temp;
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temp = x << 16;
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temp /= y;
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return (int32_t)temp;
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}
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