mirror of https://github.com/bsnes-emu/bsnes.git
26 lines
699 B
C++
26 lines
699 B
C++
#ifdef PPU_CPP
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//color addition / subtraction
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//thanks go to blargg for the optimized algorithms
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inline uint16 PPU::addsub(uint32 x, uint32 y, bool halve) {
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if(!regs.color_mode) {
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if(!halve) {
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unsigned sum = x + y;
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unsigned carry = (sum - ((x ^ y) & 0x0421)) & 0x8420;
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return (sum - carry) | (carry - (carry >> 5));
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} else {
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return (x + y - ((x ^ y) & 0x0421)) >> 1;
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}
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} else {
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unsigned diff = x - y + 0x8420;
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unsigned borrow = (diff - ((x ^ y) & 0x8420)) & 0x8420;
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if(!halve) {
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return (diff - borrow) & (borrow - (borrow >> 5));
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} else {
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return (((diff - borrow) & (borrow - (borrow >> 5))) & 0x7bde) >> 1;
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}
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}
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}
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#endif
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