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Some better looking horners save another multiplication.

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This commit is contained in:
Jorge Rodriguez 2014-07-27 00:55:47 -07:00
parent 7d47582578
commit ef3a460ec4
1 changed files with 6 additions and 12 deletions
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18
stb_resample.h
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@ -279,12 +279,10 @@ static float stbr__filter_bicubic(float x)
{ {
x = (float)fabs(x); x = (float)fabs(x);
float xx = x*x;
if (x < 1.0f) if (x < 1.0f)
return 0.5f * (x * xx) - xx + 0.66666666666f; return 0.66666666666f + x*x*(0.5f*x - 1);
else if (x < 2.0f) else if (x < 2.0f)
return -0.16666666f * (x * xx) + xx - 2 * x + 1.3333333333f; return 1.3333333333f + x*(-2 + x*(1 - 0.16666666f * x));
return (0.0f); return (0.0f);
} }
@ -293,12 +291,10 @@ static float stbr__filter_catmullrom(float x)
{ {
x = (float)fabs(x); x = (float)fabs(x);
float xx = x*x;
if (x < 1.0f) if (x < 1.0f)
return 1.5f * xx * (x - 1.66666666f) + 1; return 1 - x*x*(1.5f - 2.5f*x);
else if (x < 2.0f) else if (x < 2.0f)
return -0.5f * x * ((xx - 5 * x) + 8) + 2; return 2 - x*(4 + x*(0.5f*x - 2.5f));
return (0.0f); return (0.0f);
} }
@ -307,12 +303,10 @@ static float stbr__filter_mitchell(float x)
{ {
x = (float)fabs(x); x = (float)fabs(x);
float xx = x*x;
if (x < 1.0f) if (x < 1.0f)
return 1.1666666666666f * xx * (x - 1.714285715f) + 0.8888888888f; return 0.8888888888f + x*x*(1.1666666666666f * x - 2.0f);
else if (x < 2.0f) else if (x < 2.0f)
return -0.3888888888f * x * ((xx - 5.14285714f * x) + 8.571428571f) + 1.777777777777f; return 1.777777777777f + x*(-3.3333333333f + x*(2 - 0.3888888888888f*x));
return (0.0f); return (0.0f);
} }