This will acquire its first user in an upcoming commit.
This implementation is not optimized at all but it doesn't matter for the
purpose for which I intend to initially use it.
Signed-off-by: Ben Pfaff <b...@nicira.com>
---
lib/util.c | 29 +++++++++++++++++++++++++++++
lib/util.h | 2 ++
2 files changed, 31 insertions(+)
diff --git a/lib/util.c b/lib/util.c
index f3e47b1..01e8a0e 100644
--- a/lib/util.c
+++ b/lib/util.c
@@ -1273,6 +1273,35 @@ bitwise_is_all_zeros(const void *p_, unsigned int len,
unsigned int ofs,
return true;
}
+/* Scans the bits in 'p' that have bit offsets 'start' through 'end'
+ * (inclusive) for the first bit with value 'target'. If one is found, returns
+ * its offset, otherwise 'end'. 'p' is 'len' bytes long.
+ *
+ * If you consider all of 'p' to be a single unsigned integer in network byte
+ * order, then bit N is the bit with value 2**N. That is, bit 0 is the bit
+ * with value 1 in p[len - 1], bit 1 is the bit with value 2, bit 2 is the bit
+ * with value 4, ..., bit 8 is the bit with value 1 in p[len - 2], and so on.
+ *
+ * Required invariant:
+ * start <= end
+ */
+unsigned int
+bitwise_scan(const void *p_, unsigned int len, bool target, unsigned int start,
+ unsigned int end)
+{
+ const uint8_t *p = p_;
+ unsigned int ofs;
+
+ for (ofs = start; ofs < end; ofs++) {
+ bool bit = (p[len - (ofs / 8 + 1)] & (1u << (ofs % 8))) != 0;
+ if (bit == target) {
+ break;
+ }
+ }
+ return ofs;
+}
+
+
/* Copies the 'n_bits' low-order bits of 'value' into the 'n_bits' bits
* starting at bit 'dst_ofs' in 'dst', which is 'dst_len' bytes long.
*
diff --git a/lib/util.h b/lib/util.h
index 7da7aa8..ea9bcfa 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -503,6 +503,8 @@ void bitwise_one(void *dst_, unsigned int dst_len, unsigned
dst_ofs,
unsigned int n_bits);
bool bitwise_is_all_zeros(const void *, unsigned int len, unsigned int ofs,
unsigned int n_bits);
+unsigned int bitwise_scan(const void *, unsigned int len,
+ bool target, unsigned int start, unsigned int end);
void bitwise_put(uint64_t value,
void *dst, unsigned int dst_len, unsigned int dst_ofs,
unsigned int n_bits);
--
1.9.1
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