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z80_unpacker: optimisation: -1B in decode_number (fwd 171B / rev 168B)

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This commit is contained in:
Peter Helcmanovsky (Ped)
2022-09-19 11:49:53 +02:00
parent c1ffd0e7ed
commit db1c7d2d14
2 changed files with 5 additions and 4 deletions
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z80_unpacker/example/example.sna
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z80_unpacker/unpack.asm
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@@ -187,6 +187,9 @@ int upkr_decode_bit(int context_index) {
return bit;
}
*/
inc_c_decode_bit:
; ++low(context_index) before decode_bit (to get -1B by two calls in decode_number)
inc c
decode_bit:
; HL = upkr_state
; IX = upkr_data_ptr
@@ -298,13 +301,11 @@ decode_number:
ld de,$7FFF ; length = 0 with positional-stop-bit
jr .loop_entry
.loop:
inc c ; context_index + 1
call decode_bit
call inc_c_decode_bit ; context_index + 1
rr d
rr e ; DE = length = (length >> 1) | (bit << 15);
.loop_entry:
inc c ; context_index += 2
call decode_bit
call inc_c_decode_bit ; context_index += 2
jr c,.loop
.fix_bit_pos:
ccf ; NC will become this final `| (1 << bit_pos)` bit