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#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <errno.h>
int main(int argc, char **argv) {
if (argc != 4) {
fprintf(stderr, "usage: %s <in> <out> <image_size>\n", argv[0]);
return 1;
}
const char *in_path = argv[1];
const char *out_path = argv[2];
char *end;
errno = 0;
unsigned long long size = strtoull(argv[3], &end, 16);
if (errno || *end != '\0') {
fprintf(stderr, "bad size: %s, invalid chars: %s\n", argv[3], end);
return 1;
}
FILE *in = fopen(in_path, "rb");
if (!in) { perror("fopen in"); return 1; }
FILE *out = fopen(out_path, "wb");
if (!out) { perror("fopen out"); fclose(in); return 1; }
/* Copy in -> out */
unsigned char buf[65536];
size_t n;
while ((n = fread(buf, 1, sizeof buf, in)) > 0) {
if (fwrite(buf, 1, n, out) != n) { perror("fwrite"); return 1; }
}
if (ferror(in)) { perror("fread"); return 1; }
/* Write size as u64 little-endian at offset 16 */
unsigned char le[8];
for (int i = 0; i < 8; i++)
le[i] = (unsigned char)(size >> (8 * i));
if (fseek(out, 16, SEEK_SET) != 0) { perror("fseek"); return 1; }
if (fwrite(le, 1, 8, out) != 8) { perror("fwrite size"); return 1; }
fclose(in);
if (fclose(out) != 0) { perror("fclose out"); return 1; }
return 0;
}
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