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Update README.md
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README.md
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README.md
@ -61,7 +61,33 @@ Currently, the compile can only handle short, unmasked sequences, but it does co
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PHA ; 4 cycles
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; Total Cost = 24 cycles
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```
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## Limitations ##
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The current state representation removes data from the sparse byte array whenever a store action is queued. This prevents certain optimization that redundently store the same byte more than once, in order to minimize other operations. For example, the byte sequence `$11 $22 $22` currently generated the following, sub-optimal code sequence
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```
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TCS ; 2 cycles
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SEP #$10 ; 3 cycles
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LDA #$11 ; 2 cycles
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STA 00,s ; 4 cycles
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REP #$10 ; 3 cycles
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LDA #$2222 ; 3 cycles
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STA 01,s ; 5 cycles
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; Total Cost = 22 cycles
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```
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The optimal code sequence is
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```
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TCS ; 2 cycles
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LDA #$2211 ; 3 cycles
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STA 00,s ; 5 cycles
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LDA #$2222 ; 3 cycles
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STA 01,s ; 5 cycles
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; Total Cost = 18 cycles
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```
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Notice that byte 1 ($22) is loaded redundently, which results in the 16-bit LDA/STA code being 2 cycles slower that the equivalent 8-bit code. However, this 2-cycle penalty is more than made up for by the saving gained from avoiding the 6-cycle SEP/REP pair in order to enter and exit 8-bit mode, resulting in a net savings of 4 cycles.
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## License
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MIT License
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