diff options
Diffstat (limited to 'baremetal/115write-byte.subx')
| -rw-r--r-- | baremetal/115write-byte.subx | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/baremetal/115write-byte.subx b/baremetal/115write-byte.subx new file mode 100644 index 00000000..32245116 --- /dev/null +++ b/baremetal/115write-byte.subx @@ -0,0 +1,37 @@ +# instruction effective address register displacement immediate +# . op subop mod rm32 base index scale r32 +# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes + +# Write lower byte of 'n' to 'f'. +append-byte: # f: (addr stream byte), n: int + # . prologue + 55/push-ebp + 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp + # . save registers + 51/push-ecx + 57/push-edi + # edi = f + 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 7/r32/edi 8/disp8 . # copy *(ebp+8) to edi + # ecx = f->write + 8b/copy 0/mod/indirect 7/rm32/edi . . . 1/r32/ecx . . # copy *edi to ecx + # if (f->write >= f->size) abort + 3b/compare 1/mod/*+disp8 7/rm32/edi . . . 1/r32/ecx 8/disp8 . # compare ecx with *(edi+8) + 7d/jump-if->= $append-byte:end/disp8 # TODO: abort +$append-byte:to-stream: + # write to stream + # f->data[f->write] = LSB(n) + 31/xor 3/mod/direct 0/rm32/eax . . . 0/r32/eax . . # clear eax + 8a/copy-byte 1/mod/*+disp8 5/rm32/ebp . . . 0/r32/AL 0xc/disp8 . # copy byte at *(ebp+12) to AL + 88/copy-byte 1/mod/*+disp8 4/rm32/sib 7/base/edi 1/index/ecx . 0/r32/AL 0xc/disp8 . # copy AL to *(edi+ecx+12) + # ++f->write + ff 0/subop/increment 0/mod/indirect 7/rm32/edi . . . . . . # increment *edi +$append-byte:end: + # . restore registers + 5f/pop-to-edi + 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 + +# . . vim:nowrap:textwidth=0 |