Difference between revisions of "Z80 Routines:Optimized:PopCountA"
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(Created page with "PopCountA PopCountA This is a faster/smaller (and also obfuscated) replacement for the normal popcount a, which r...") |
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| Line 8: | Line 8: | ||
;27 bytes, 108 clock cycles | ;27 bytes, 108 clock cycles | ||
TypicalPopCountA: | TypicalPopCountA: | ||
| − | |||
xor a | xor a | ||
| − | ld | + | ld c, a |
| − | rrc | + | rrc b |
| − | adc a, | + | adc a, c |
| − | rrc | + | rrc b |
| − | adc a, | + | adc a, c |
| − | rrc | + | rrc b |
| − | adc a, | + | adc a, c |
| − | rrc | + | rrc b |
| − | adc a, | + | adc a, c |
| − | rrc | + | rrc b |
| − | adc a, | + | adc a, c |
| − | rrc | + | rrc b |
| − | adc a, | + | adc a, c |
| − | rrc | + | rrc b |
| − | adc a, | + | adc a, c |
| − | rrc | + | rrc b |
| − | adc a, | + | adc a, c</nowiki> |
Better routine: | Better routine: | ||
| Line 36: | Line 35: | ||
;author: jacobly | ;author: jacobly | ||
PopCountA: | PopCountA: | ||
| − | ld c, a | + | ld c, a ; c=(A|B|C|D|E|F|G|H) |
| − | and 10101010b | + | and 10101010b ; a=(A|0|C|0|E|0|G|0) |
| − | cpl | + | cpl ; a=(~A|1|~C|1|~E|1|~G|1) |
| − | rrca | + | rrca ; a=(1|~A|1|~C|1|~E|1|~G), cf=1 |
| − | adc a, c | + | adc a, c ; a=(A+B|C+D|E+F|G+H) |
| − | ld b, a | + | ld b, a ; b=(A+B|C+D|E+F|G+H) |
| − | and 00110011b | + | and 00110011b ; a=(00|C+D|00|G+H) |
| − | ld c, a | + | ld c, a ; c=(00|C+D|00|G+H) |
| − | xor b | + | xor b ; a=(A+B|00|E+F|00) |
| − | rrca | + | rrca \ rrca ; a=(0|A+B|00|E+F|0) |
| − | + | add a, c ; a=(A+B+C+D|E+F+G+H) | |
| − | add a, c | + | ld c, a ; c=(A+B+C+D|E+F+G+H) |
| − | ld c, a | + | rrca \ rrca \ rrca \ rrca ; a=(E+F+G+H|A+B+C+D) |
| − | rrca | + | add a, c ; a=(A+B+C+D+E+F+G+H|A+B+C+D+E+F+G+H) |
| − | + | and 00001111b ; a=A+B+C+D+E+F+G+H</nowiki> | |
| − | + | ||
| − | + | ||
| − | add a, c | + | |
| − | and 00001111b</nowiki> | + | |
Revision as of 19:35, 15 September 2020
This is a faster/smaller (and also obfuscated) replacement for the normal popcount a, which returns the number of set bits in a.
Typical routine:
;input: b ;output: a ;27 bytes, 108 clock cycles TypicalPopCountA: xor a ld c, a rrc b adc a, c rrc b adc a, c rrc b adc a, c rrc b adc a, c rrc b adc a, c rrc b adc a, c rrc b adc a, c rrc b adc a, c
Better routine:
;- Pop Count A ;input: byte in A ;output: number of set bits in A ;destroys BC ;22 bytes and 85 clock cycles ;author: jacobly PopCountA: ld c, a ; c=(A|B|C|D|E|F|G|H) and 10101010b ; a=(A|0|C|0|E|0|G|0) cpl ; a=(~A|1|~C|1|~E|1|~G|1) rrca ; a=(1|~A|1|~C|1|~E|1|~G), cf=1 adc a, c ; a=(A+B|C+D|E+F|G+H) ld b, a ; b=(A+B|C+D|E+F|G+H) and 00110011b ; a=(00|C+D|00|G+H) ld c, a ; c=(00|C+D|00|G+H) xor b ; a=(A+B|00|E+F|00) rrca \ rrca ; a=(0|A+B|00|E+F|0) add a, c ; a=(A+B+C+D|E+F+G+H) ld c, a ; c=(A+B+C+D|E+F+G+H) rrca \ rrca \ rrca \ rrca ; a=(E+F+G+H|A+B+C+D) add a, c ; a=(A+B+C+D+E+F+G+H|A+B+C+D+E+F+G+H) and 00001111b ; a=A+B+C+D+E+F+G+H
