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games/mix: fix implementation of MOVE instruction (thanks nicolagi)

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Plan 9 memcpy(2) uses the same implementation as memmove(2) to handle
overlapping ranges.  Hovewer, the MIX MOVE instruction, as described
in TAOCP, specifically does not do this.  It copies words one at a
time starting from the lowest address.

This change also expands the address validation to check that all
addresses within the source and destination ranges are valid before
proceeding.
This commit is contained in:
Alex Musolino 2020-11-27 11:19:49 +10:30
parent 781a8f8d9f
commit 2a907fd459
1 changed files with 10 additions and 4 deletions
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14
sys/src/games/mix/mix.c
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@ -729,14 +729,20 @@ void
mixmove(int s, int f)
{
int d;
u32int *p, *q, *pe;
if(f == 0)
return;
if(s < 0 || s >= 4000 || s+f < 0 || s+f > 4000)
vmerror("Bad src range MOVE %d:%d", s, s+f-1);
d = mval(ri[1], 0, MASK2);
if(d < 0 || d > 4000)
vmerror("Bad address MOVE %d", d);
memcpy(cells+d, cells+s, f*sizeof(u32int));
if(d < 0 || d >= 4000 || d+f < 0 || d+f > 4000)
vmerror("Bad dst range MOVE %d:%d", d, d+f-1);
p = cells+d;
q = cells+s;
pe = p+f;
while(p < pe)
*p++ = *q++;
d += f;
d &= MASK2;
ri[1] = d < 0 ? -d|SIGNB : d;