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Use nibbilized size for dest; allow offset to overflow

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This commit is contained in:
Peter Evans 2018-01-31 14:28:29 -06:00
parent 7ffe2cb527
commit c031822063
1 changed files with 17 additions and 11 deletions
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28
src/apple2.enc.c
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@ -3,6 +3,7 @@
*/
#include "apple2.enc.h"
#include "apple2.dd.h"
#include "vm_segment.h"
static vm_8bit gcr62[] = {
@ -19,22 +20,19 @@ apple2_enc_dos(vm_segment *src)
vm_segment *dest;
int i, doff = 0;
// FIXME: we need to find the actual size of a nibble-ized DO/PO
// order file
dest = vm_segment_create(500000);
// Use the nibbilized size for a 140k image file
dest = vm_segment_create(_140K_NIB_);
for (i = 0; i < 35; i++) {
doff += apple2_enc_track(dest, src, doff, i);
}
printf("len = %d\n", doff);
return dest;
}
int
apple2_enc_track(vm_segment *dest, vm_segment *src,
int doff, int track)
int doff, int track)
{
int soff = track * 4096;
int orig = doff;
@ -53,7 +51,7 @@ apple2_enc_track(vm_segment *dest, vm_segment *src,
doff += apple2_enc_sector(dest, src, doff, soff);
// We're moving here in 256-byte blocks
soff += sect * 256;
soff += 256;
}
return doff - orig;
@ -68,7 +66,7 @@ apple2_enc_track(vm_segment *dest, vm_segment *src,
*/
int
apple2_enc_sector(vm_segment *dest, vm_segment *src,
int doff, int soff)
int doff, int soff)
{
int i, di, orig;
vm_8bit lastval, curval;
@ -86,15 +84,23 @@ apple2_enc_sector(vm_segment *dest, vm_segment *src,
// initial array.
for (i = 0; i < 0x56; i++) {
vm_8bit v = 0, vac, v56, v00;
vm_8bit offac, off56;
// We compute the offsets for the values beginning at ac and 56
// here, specifically in 8bit variables, because we _want_ any
// overflow to be handled within the offset rather than spilling
// beyond the border of the segment.
offac = i + 0xAC;
off56 = i + 0x56;
// We do the write by working with the src segment in rough
// thirds. vac is the value offset by 0xAC, which is 0x56 * 2.
// v56 is offset by 0x56, and v00 has no offset. In decimal
// terms, vac is 172 bytes offset from 0, and v56 is 86 bytes
// offset from 0.
vac = vm_segment_get(src, soff+i+0xAC);
v56 = vm_segment_get(src, soff+i+0x56);
v00 = vm_segment_get(src, soff+i);
vac = vm_segment_get(src, soff + offac);
v56 = vm_segment_get(src, soff + off56);
v00 = vm_segment_get(src, soff + i);
// The value we ultimately want to write into the dest segment
// is then mangled a bit. v begins life as zero, of course; it's