diff options
| -rw-r--r-- | qemu-img.c | 29 |
1 files changed, 26 insertions, 3 deletions
diff --git a/qemu-img.c b/qemu-img.c index 1da5484ff0..4f162d1abe 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -496,14 +496,37 @@ static int img_commit(int argc, char **argv) return 0; } +/* + * Checks whether the sector is not a zero sector. + * + * Attention! The len must be a multiple of 4 * sizeof(long) due to + * restriction of optimizations in this function. + */ static int is_not_zero(const uint8_t *sector, int len) { + /* + * Use long as the biggest available internal data type that fits into the + * CPU register and unroll the loop to smooth out the effect of memory + * latency. + */ + int i; - len >>= 2; - for(i = 0;i < len; i++) { - if (((uint32_t *)sector)[i] != 0) + long d0, d1, d2, d3; + const long * const data = (const long *) sector; + + len /= sizeof(long); + + for(i = 0; i < len; i += 4) { + d0 = data[i + 0]; + d1 = data[i + 1]; + d2 = data[i + 2]; + d3 = data[i + 3]; + + if (d0 || d1 || d2 || d3) { return 1; + } } + return 0; } |