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14 lines
409 B
C
14 lines
409 B
C
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#include "neslib.h"
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word bcd_add(word a, word b) {
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register word c, d; // intermediate values
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c = a + 0x0666; // add 6 to each BCD digit
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d = c ^ b; // sum without carry propagation
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c += b; // provisional sum
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d = ~(c ^ d) & 0x1110; // just the BCD carry bits
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d = (d >> 2) | (d >> 3); // correction
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return c - d; // corrected BCD sum
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}
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