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add a redundant loop condition to silence GCC warnings 

See:
https://github.com/BLAKE3-team/BLAKE3/issues/94
https://github.com/BLAKE3-team/BLAKE3/issues/183
https://github.com/BLAKE3-team/BLAKE3/issues/189
This commit is contained in:
Jack O'Connor 2021-08-12 15:19:50 -04:00
parent 32758e34a4
commit b8e2dda186
1 changed files with 7 additions and 1 deletions
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8
c/blake3.c
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@ -340,12 +340,18 @@ INLINE void compress_subtree_to_parent_node(
uint8_t cv_array[MAX_SIMD_DEGREE_OR_2 * BLAKE3_OUT_LEN];
size_t num_cvs = blake3_compress_subtree_wide(input, input_len, key,
chunk_counter, flags, cv_array);
assert(num_cvs <= MAX_SIMD_DEGREE_OR_2);
// If MAX_SIMD_DEGREE is greater than 2 and there's enough input,
// compress_subtree_wide() returns more than 2 chaining values. Condense
// them into 2 by forming parent nodes repeatedly.
uint8_t out_array[MAX_SIMD_DEGREE_OR_2 * BLAKE3_OUT_LEN / 2];
while (num_cvs > 2) {
// The second half of this loop condition is always true, and we just
// asserted it above. But GCC can't tell that it's always true, and if NDEBUG
// is set on platforms where MAX_SIMD_DEGREE_OR_2 == 2, GCC emits spurious
// warnings here. GCC 8.5 is particular sensitive, so if you're changing this
// code, test it against that version.
while (num_cvs > 2 && num_cvs <= MAX_SIMD_DEGREE_OR_2) {
num_cvs =
compress_parents_parallel(cv_array, num_cvs, key, flags, out_array);
memcpy(cv_array, out_array, num_cvs * BLAKE3_OUT_LEN);