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strncat: fix more issues related to large n values.

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This addresses the following issues:
*If the low-order 16 bits of n were 0x0000, no concatenation would be performed.
*If n was 0x1000000 or greater, the output could be cut off prematurely because the high byte of n was effectively ignored.

The following test program demonstrates these issues:

#pragma memorymodel 1
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#define LEN2 100000
int main(void) {
        char *s1 = malloc(LEN2+2);
        char *s2 = malloc(LEN2+1);
        if (!s1 || !s2)
                return 0;
        for (unsigned long i = 0; i < LEN2; i++)
                s2[i] = '0' + (i & 0x07);
        strcpy(s1,"a");
        strncat(s1, s2, 0x1000000);
        puts(s1);
        printf("len = %zu\n", strlen(s1));
}
This commit is contained in:
Stephen Heumann 2024-02-19 22:01:53 -06:00
parent f1582be5a2
commit bbfad1e299
1 changed files with 12 additions and 8 deletions
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20
string.asm
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@ -1017,29 +1017,33 @@ lb2 long M
sta s1
bcc lb2a
inc s1+2
lb2a short M copy characters 'til the null is found
lb2a ldx n copy characters 'til the null is found
bne lb2b
lda n+2
beq lb6
lb2b short M
ldy #0
ldx n
beq lb4
lb3 lda [s2],Y
sta [s1],Y
beq lb4
beq lb5
iny
bne lb3a
inc s1+2
inc s2+2
lb3a dex
bne lb3
lda n+2
ldx n+2
beq lb4
dec n+2
dex
stx n+2
ldx #0
bra lb3
lb4 lda #0 write the terminating null
sta [s1],Y
long M return to the caller
lb5 long M return to the caller
creturn 4:rval
lb6 creturn 4:rval
end
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