this adds buffer_find_nonzero_offset() which is a SSE2/Altivec
optimized function that searches for non-zero content in a
buffer.
due to the optimizations used in the function there are restrictions
on buffer address and search length. the function
can_use_buffer_find_nonzero_content() can be used to check if
the function can be used safely.
Signed-off-by: Peter Lieven <p...@kamp.de>
---
include/qemu-common.h | 13 +++++++++++++
util/cutils.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 58 insertions(+)
diff --git a/include/qemu-common.h b/include/qemu-common.h
index e76ade3..078e535 100644
--- a/include/qemu-common.h
+++ b/include/qemu-common.h
@@ -472,4 +472,17 @@ 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)
+{
+ if (len % (BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR
+ * sizeof(VECTYPE)) == 0
+ && ((uintptr_t) buf) % sizeof(VECTYPE) == 0) {
+ return true;
+ }
+ return false;
+}
+size_t buffer_find_nonzero_offset(const void *buf, size_t len);
+
#endif
diff --git a/util/cutils.c b/util/cutils.c
index 1439da4..41c627e 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -143,6 +143,51 @@ 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 BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR * sizeof(VECTYPE).
+ * 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)
+{
+ VECTYPE *p = (VECTYPE *)buf;
+ VECTYPE zero = ZERO_SPLAT;
+ size_t i;
+
+ assert(len % (BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR
+ * sizeof(VECTYPE)) == 0);
+ assert(((uintptr_t) buf) % sizeof(VECTYPE) == 0);
+
+ if (*((const long *) buf)) {
+ return 0;
+ }
+
+ for (i = 0; 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
--
1.7.9.5
