Hi!
* Bernard Fouché <bernard.fou...@kuantic.com> [10-05-19 17:06]:
[reordered quote]
> >>>//
> >>>---------------------------------------------------------------------------
> >>>void xteaDecrypt(uint32_t v[2], uint32_t const k[4]) {
> >>> uint32_t v0=v[0], v1=v[1], delta=0x9E3779B9, sum=delta*XTEA_ROUNDS;
> >>> for (uint8_t i=0; i< XTEA_ROUNDS; i++) {
> >>> v1 -= (((v0<< 4) ^ (v0>> 5)) + v0) ^ (sum + k[(sum>>11)& 3]);
> >>> sum -= delta;
> >>> v0 -= (((v1<< 4) ^ (v1>> 5)) + v1) ^ (sum + k[sum& 3]);
> >>> }
> >>> v[0]=v0; v[1]=v1;
> >>>}
> >>>
> >>>void xteaDecryptCbc(uint8_t v[8], uint8_t cb[8], uint8_t const k[16]) {
> >>> static uint8_t tmpbuf[8];
> >>> memcpy(tmpbuf, v, 8);
> >>> xteaDecrypt((uint32_t*)v, (uint32_t*)k);
> >>> for (uint8_t i=0; i< 8; i++)
> >>> v[i] ^= cb[i];
> >>> memcpy(cb, tmpbuf, 8);
> >>>}
> >>>
> >>>int main(void) {
> >>> uint8_t b1[8], b2[8], b3[16];
> >>> xteaDecryptCbc(b1, b2 b3);
> >>>}
> >>>//
> >>>---------------------------------------------------------------------------
>
> I don't understand what 'tmpbuf' is declared 'static'.
tmpbuf is declared static as the compiler produces better code in this
case (arrays on the stack are costly).
> And what do you mean by 'broken'? In your example, main() calls
> functions by providing pointers to uninitialized data located in the
> stack.
This was just an incomplete example, in my application those buffers are
filled with real data. I provided the declarations in main() because for
alias analysis the declared type of a variable matters.
-- Lars.
_______________________________________________
AVR-GCC-list mailing list
AVR-GCC-list@nongnu.org
http://lists.nongnu.org/mailman/listinfo/avr-gcc-list
