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Justine Tunney 2020-06-15 07:18:57 -07:00
commit c91b3c5006
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dsp/core/c1331.h Normal file
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#ifndef COSMOPOLITAN_DSP_CORE_C1331_H_
#define COSMOPOLITAN_DSP_CORE_C1331_H_
#if !(__ASSEMBLER__ + __LINKER__ + 0)
/**
* Byte sized kernel for resampling memory in half.
*
* @define (1*𝑎 + 3*𝑏 + 3*𝑐 + 1*𝑑) / (1 + 3 + 3 + 1)
* @see C161() afterward for superior sin(𝑥)/𝑥
* @limit [0,255] → [0..2,044] → [0..255]
*/
forceinline pureconst artificial unsigned char C1331(unsigned char al,
unsigned char bl,
unsigned char cl,
unsigned char dl) {
short ax, bx;
bx = bl;
bx += cl;
bx *= 3;
ax = al;
ax += dl;
ax += bx;
ax += 4;
ax >>= 3;
al = ax;
return al;
}
#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
#endif /* COSMOPOLITAN_DSP_CORE_C1331_H_ */