diff options
Diffstat (limited to 'util')
-rw-r--r-- | util/bitops.c | 18 | ||||
-rw-r--r-- | util/cutils.c | 60 |
2 files changed, 77 insertions, 1 deletions
diff --git a/util/bitops.c b/util/bitops.c index e72237ab2b..227c38b883 100644 --- a/util/bitops.c +++ b/util/bitops.c @@ -42,7 +42,23 @@ unsigned long find_next_bit(const unsigned long *addr, unsigned long size, size -= BITS_PER_LONG; result += BITS_PER_LONG; } - while (size & ~(BITS_PER_LONG-1)) { + while (size >= 4*BITS_PER_LONG) { + unsigned long d1, d2, d3; + tmp = *p; + d1 = *(p+1); + d2 = *(p+2); + d3 = *(p+3); + if (tmp) { + goto found_middle; + } + if (d1 | d2 | d3) { + break; + } + p += 4; + result += 4*BITS_PER_LONG; + size -= 4*BITS_PER_LONG; + } + while (size >= BITS_PER_LONG) { if ((tmp = *(p++))) { goto found_middle; } diff --git a/util/cutils.c b/util/cutils.c index 1439da4f99..5024253405 100644 --- a/util/cutils.c +++ b/util/cutils.c @@ -143,6 +143,61 @@ int qemu_fdatasync(int fd) } /* + * Searches for an area with non-zero content in a buffer + * + * Attention! The len must be a multiple of + * BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR * sizeof(VECTYPE) + * and addr must be a multiple of sizeof(VECTYPE) due to + * restriction of optimizations in this function. + * + * can_use_buffer_find_nonzero_offset() can be used to check + * these requirements. + * + * The return value is the offset of the non-zero area rounded + * down to a multiple of sizeof(VECTYPE) for the first + * BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR chunks and down to + * BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR * sizeof(VECTYPE) + * afterwards. + * + * If the buffer is all zero the return value is equal to len. + */ + +size_t buffer_find_nonzero_offset(const void *buf, size_t len) +{ + const VECTYPE *p = buf; + const VECTYPE zero = (VECTYPE){0}; + size_t i; + + assert(can_use_buffer_find_nonzero_offset(buf, len)); + + if (!len) { + return 0; + } + + for (i = 0; i < BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR; i++) { + if (!ALL_EQ(p[i], zero)) { + return i * sizeof(VECTYPE); + } + } + + for (i = BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR; + i < len / sizeof(VECTYPE); + i += BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR) { + VECTYPE tmp0 = p[i + 0] | p[i + 1]; + VECTYPE tmp1 = p[i + 2] | p[i + 3]; + VECTYPE tmp2 = p[i + 4] | p[i + 5]; + VECTYPE tmp3 = p[i + 6] | p[i + 7]; + VECTYPE tmp01 = tmp0 | tmp1; + VECTYPE tmp23 = tmp2 | tmp3; + if (!ALL_EQ(tmp01 | tmp23, zero)) { + break; + } + } + + return i * sizeof(VECTYPE); +} + +/* * Checks if a buffer is all zeroes * * Attention! The len must be a multiple of 4 * sizeof(long) due to @@ -160,6 +215,11 @@ bool buffer_is_zero(const void *buf, size_t len) long d0, d1, d2, d3; const long * const data = buf; + /* use vector optimized zero check if possible */ + if (can_use_buffer_find_nonzero_offset(buf, len)) { + return buffer_find_nonzero_offset(buf, len) == len; + } + assert(len % (4 * sizeof(long)) == 0); len /= sizeof(long); |