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| author | inmarket <andrewh@inmarket.com.au> | 2013-09-24 16:11:29 +1000 |
|---|---|---|
| committer | inmarket <andrewh@inmarket.com.au> | 2013-09-24 16:11:29 +1000 |
| commit | d704c2f6d05ecaffa644213f728ed2d0182eeaee (patch) | |
| tree | 896cd0067546963fe32e8ec97dfdb9c892038f42 /src | |
| parent | 973e34089e33f06cfd9ed560db968870e22c2b8a (diff) | |
| download | uGFX-d704c2f6d05ecaffa644213f728ed2d0182eeaee.tar.gz uGFX-d704c2f6d05ecaffa644213f728ed2d0182eeaee.tar.bz2 uGFX-d704c2f6d05ecaffa644213f728ed2d0182eeaee.zip | |
New inverse square root accelerated math function
Diffstat (limited to 'src')
| -rw-r--r-- | src/gmisc/trig.c | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/src/gmisc/trig.c b/src/gmisc/trig.c index 510ee597..00b6365a 100644 --- a/src/gmisc/trig.c +++ b/src/gmisc/trig.c @@ -142,5 +142,23 @@ #endif +#if GMISC_NEED_INVSQRT + // Algorithm based on Quake code + float invsqrt(float n) { + long i; + float x2, y; + const float threehalfs = 1.5F; + + x2 = n * 0.5F; + y = n; + i = * ( long * ) &y; // evil floating point bit level hacking + i = 0x5f3759df - ( i >> 1 ); // what the? + y = * ( float * ) &i; + y = y * ( threehalfs - ( x2 * y * y ) ); // 1st iteration + //y = y * ( threehalfs - ( x2 * y * y ) ); // 2nd iteration for extra precision, this can be removed + return y; + } +#endif + #endif /* GFX_USE_GMISC */ /** @} */ |