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5142 

Hoist address computation out of the loop.

I'm giving in to the temptation to optimize here, and violating my own
rule of minimizing local variables by introducing 'curr'. My fig leaf is
that the number of instructions inside the loop goes down, and duplicating
inside the loop may be distracting to readers.
This commit is contained in:
Kartik Agaram 2019-05-04 14:39:45 -07:00
parent 85a3e39cd5
commit 37aa2bf3e8
1 changed files with 20 additions and 12 deletions
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32
subx/074print-int-decimal.subx
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@ -25,11 +25,15 @@ print-int32-decimal: # out : (address stream), n : int32
# if (EAX == 0) break
# if n < 0
# push '-'
# w = out->write
# curr = &out->data[out->write]
# while true
# pop into EAX
# if (EAX == sentinel) break
# out->data[out->write] = AL
# ++out->write
# *curr = AL
# ++curr
# ++w
# out->write = w
# (based on K&R itoa: https://en.wikibooks.org/wiki/C_Programming/stdlib.h/itoa)
# (this pseudocode contains registers because operations like division
# require specific registers in x86)
@ -47,7 +51,7 @@ print-int32-decimal: # out : (address stream), n : int32
# push sentinel
68/push 0/imm32/sentinel
# EAX = abs(n)
8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 0/r32/EAX 0xc/disp8 . # EAX = *(EBP+12)
8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 0/r32/EAX 0xc/disp8 . # copy *(EBP+12) to EAX
3d/compare-EAX-with 0/imm32
7d/jump-if-greater-or-equal $print-int32-decimal:read-loop/disp8
f7 3/subop/negate 3/mod/direct 0/rm32/EAX . . . . . . # negate EAX
@ -70,22 +74,26 @@ $print-int32-decimal:read-break:
$print-int32-decimal:write:
# EDI = out
8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 7/r32/EDI 8/disp8 . # copy *(EBP+8) to EDI
# w/EDX = out->write
8b/copy 0/mod/indirect 7/rm32/EDI . . . 2/r32/EDX . . # copy *EDI to EDX
# curr/ECX = &out->data[out->write]
8d/copy-address 1/mod/*+disp8 4/rm32/sib 7/base/EDI 2/index/EDX . 1/r32/ECX 0xc/disp8 . # copy EBX+EDX+12 to ECX
$print-int32-decimal:write-loop:
# pop into EAX
58/pop-to-EAX
# if (EAX == sentinel) break
3d/compare-EAX-and 0/imm32/sentinel
74/jump-if-equal $print-int32-decimal:end/disp8
# out->data[out->write] = AL
# . ECX = out->write
8b/copy 0/mod/indirect 7/rm32/EDI . . . 1/r32/ECX . . # copy *EDI to ECX
# . ECX = &out->data[out->write]
8d/copy-address 1/mod/*+disp8 4/rm32/sib 7/base/EDI 1/index/ECX . 1/r32/ECX 0xc/disp8 . # copy EBX+ECX+12 to ECX
# . out->data[out->write] = AL
74/jump-if-equal $print-int32-decimal:write-break/disp8
# *curr = AL
88/copy-byte 0/mod/indirect 1/rm32/ECX . . . 0/r32/AL . . # copy AL to byte at *ECX
# out->write++
ff 0/subop/increment 0/mod/indirect 7/rm32/EDI . . . . . . # increment *EDI
# ++curr
41/increment-ECX
# ++w
42/increment-EDX
eb/jump $print-int32-decimal:write-loop/disp8
$print-int32-decimal:write-break:
# out->write = w
89/copy 0/mod/indirect 7/rm32/EDI . . . 2/r32/EDX . . # copy EDX to *EDI
$print-int32-decimal:end:
# . restore registers
5f/pop-to-EDI