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Add utility function 'memxor'.

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This commit is contained in:
Simon Tatham 2021-02-20 16:47:52 +00:00
parent 09fa3f0e80
commit 609502b04b
2 changed files with 35 additions and 0 deletions
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9
misc.h
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@ -430,4 +430,13 @@ LoadFileStatus lf_load(LoadedFile *lf, const Filename *filename);
static inline ptrlen ptrlen_from_lf(LoadedFile *lf)
{ return make_ptrlen(lf->data, lf->len); }
/* Set the memory block of 'size' bytes at 'out' to the bitwise XOR of
* the two blocks of the same size at 'in1' and 'in2'.
*
* 'out' may point to exactly the same address as one of the inputs,
* but if the input and output blocks overlap in any other way, the
* result of this function is not guaranteed. No memmove-style effort
* is made to handle difficult overlap cases. */
void memxor(uint8_t *out, const uint8_t *in1, const uint8_t *in2, size_t size);
#endif

26
utils.c
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@ -1073,3 +1073,29 @@ void write_c_string_literal(FILE *fp, ptrlen str)
fprintf(fp, "\\%03o", (unsigned char)c);
}
}
void memxor(uint8_t *out, const uint8_t *in1, const uint8_t *in2, size_t size)
{
switch (size & 15) {
case 0:
while (size >= 16) {
*out++ = *in1++ ^ *in2++;
case 15: *out++ = *in1++ ^ *in2++;
case 14: *out++ = *in1++ ^ *in2++;
case 13: *out++ = *in1++ ^ *in2++;
case 12: *out++ = *in1++ ^ *in2++;
case 11: *out++ = *in1++ ^ *in2++;
case 10: *out++ = *in1++ ^ *in2++;
case 9: *out++ = *in1++ ^ *in2++;
case 8: *out++ = *in1++ ^ *in2++;
case 7: *out++ = *in1++ ^ *in2++;
case 6: *out++ = *in1++ ^ *in2++;
case 5: *out++ = *in1++ ^ *in2++;
case 4: *out++ = *in1++ ^ *in2++;
case 3: *out++ = *in1++ ^ *in2++;
case 2: *out++ = *in1++ ^ *in2++;
case 1: *out++ = *in1++ ^ *in2++;
size -= 16;
}
}
}