diff --git a/include/qemu-common.h b/include/qemu-common.h index d7ad3a70f1..31fff22f32 100644 --- a/include/qemu-common.h +++ b/include/qemu-common.h @@ -469,4 +469,14 @@ void hexdump(const char *buf, FILE *fp, const char *prefix, size_t size); #define ALL_EQ(v1, v2) ((v1) == (v2)) #endif +#define BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR 8 +static inline bool +can_use_buffer_find_nonzero_offset(const void *buf, size_t len) +{ + return (len % (BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR + * sizeof(VECTYPE)) == 0 + && ((uintptr_t) buf) % sizeof(VECTYPE) == 0); +} +size_t buffer_find_nonzero_offset(const void *buf, size_t len); + #endif diff --git a/util/cutils.c b/util/cutils.c index 1439da4f99..0696a3ba5e 100644 --- a/util/cutils.c +++ b/util/cutils.c @@ -142,6 +142,61 @@ int qemu_fdatasync(int fd) #endif } +/* + * 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 *