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| author | Kartik K. Agaram <vc@akkartik.com> | 2021-08-10 05:52:48 -0700 |
|---|---|---|
| committer | Kartik K. Agaram <vc@akkartik.com> | 2021-08-10 05:52:48 -0700 |
| commit | e72e5ad2977c054790426722d5809c0a8e5f1307 (patch) | |
| tree | 99813fe61b5f6424230bfc8ec2b6c9f7875cf1e6 /112read-byte.subx | |
| parent | ed068e859d1ba9cd466c0356799cfeba44704cfe (diff) | |
| download | mu-e72e5ad2977c054790426722d5809c0a8e5f1307.tar.gz | |
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Diffstat (limited to '112read-byte.subx')
| -rw-r--r-- | 112read-byte.subx | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/112read-byte.subx b/112read-byte.subx index 93503d8b..5ffd4903 100644 --- a/112read-byte.subx +++ b/112read-byte.subx @@ -42,6 +42,38 @@ $read-byte:abort: (abort "read-byte: empty stream") # never gets here +# Return next byte value in eax, with top 3 bytes cleared. +# Abort on reaching end of stream. +peek-byte: # s: (addr stream byte) -> result/eax: byte + # . prologue + 55/push-ebp + 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp + # . save registers + 51/push-ecx + 56/push-esi + # esi = s + 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 6/r32/esi 8/disp8 . # copy *(ebp+8) to esi + # ecx = s->read + 8b/copy 1/mod/*+disp8 6/rm32/esi . . . 1/r32/ecx 4/disp8 . # copy *(esi+4) to ecx + # if (f->read >= f->write) abort + 3b/compare 0/mod/indirect 6/rm32/esi . . . 1/r32/ecx . . # compare ecx with *esi + 0f 8d/jump-if->= $peek-byte:abort/disp32 + # result = f->data[f->read] + 31/xor 3/mod/direct 0/rm32/eax . . . 0/r32/eax . . # clear eax + 8a/copy-byte 1/mod/*+disp8 4/rm32/sib 6/base/esi 1/index/ecx . 0/r32/AL 0xc/disp8 . # copy byte at *(esi+ecx+12) to AL +$peek-byte:end: + # . restore registers + 5e/pop-to-esi + 59/pop-to-ecx + # . epilogue + 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp + 5d/pop-to-ebp + c3/return + +$peek-byte:abort: + (abort "peek-byte: empty stream") + # never gets here + == data _test-input-stream: # (stream byte) |