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Code Issues 1 Releases Wiki Activity

eliminate large stack allocation from arc4random_buf bodge

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Jason Pepas 2020-06-30 04:06:20 -05:00
parent 597d84e263
commit f5d208d5d6
1 changed files with 11 additions and 6 deletions
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17
src/core/os.c
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@ -72,15 +72,20 @@ void arc4random_buf(void *buf, size_t nbytes);
/* arc4random_buf wasn't available in OS X until 10.7. */
#ifdef JANET_NO_ARC4RANDOM_BUF
/* Based on https://stackoverflow.com/a/12956868/558735 */
uint32_t arc4random(void);
void arc4random_buf(void *buf, size_t nbytes) {
size_t entropy_len = (nbytes/4)+1;
uint32_t entropy[entropy_len];
for (size_t i = 0; i < entropy_len; i++) {
entropy[i] = arc4random();
uint32_t *buf_as_words = (uint32_t*)buf;
size_t nwords = nbytes / 4;
for (size_t i=0; i < nwords; i++) {
buf_as_words[i] = arc4random();
}
size_t tail_len = nbytes % 4;
if (tail_len) {
uint8_t *tail = buf + nbytes - tail_len;
uint32_t rand = arc4random();
memcpy(tail, &rand, tail_len);
}
memcpy(buf, entropy, nbytes);
}
#endif