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31 lines
856 B
C
31 lines
856 B
C
#ifndef COSMOPOLITAN_DSP_CORE_C1331_H_
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#define COSMOPOLITAN_DSP_CORE_C1331_H_
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#if !(__ASSEMBLER__ + __LINKER__ + 0)
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/**
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* Byte sized kernel for resampling memory in half.
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*
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* @define (1*𝑎 + 3*𝑏 + 3*𝑐 + 1*𝑑) / (1 + 3 + 3 + 1)
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* @see C161() afterward for superior sin(𝑥)/𝑥
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* @limit [0,255] → [0..2,044] → [0..255]
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*/
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forceinline pureconst artificial unsigned char C1331(unsigned char al,
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unsigned char bl,
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unsigned char cl,
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unsigned char dl) {
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short ax, bx;
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bx = bl;
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bx += cl;
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bx *= 3;
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ax = al;
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ax += dl;
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ax += bx;
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ax += 4;
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ax >>= 3;
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al = ax;
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return al;
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}
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#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
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#endif /* COSMOPOLITAN_DSP_CORE_C1331_H_ */
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