Signed-off-by: Ben Pfaff <b...@nicira.com>
---
lib/util.c | 46 +++++++++++++++++++++++++++++++++++++++++++++-
lib/util.h | 4 +++-
2 files changed, 48 insertions(+), 2 deletions(-)
diff --git a/lib/util.c b/lib/util.c
index 7114d9f..e52c526 100644
--- a/lib/util.c
+++ b/lib/util.c
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
+ * Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira Networks.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
@@ -799,6 +799,50 @@ bitwise_copy(const void *src_, unsigned int src_len,
unsigned int src_ofs,
}
}
+/* Zeros the 'n_bits' bits starting from bit 'dst_ofs' in 'dst'. 'dst' is
+ * 'dst_len' bytes long. Bit 0 of 'dst' is the bit with value 1 in dst[dst_len
+ * - 1], bit 1 is the bit with value 2, bit 8 is the bit with value 1 in
+ * dst[dst_len - 2], and so on.
+ *
+ * Required invariant:
+ * dst_ofs + n_bits <= dst_len * 8
+ */
+void
+bitwise_zero(void *dst_, unsigned int dst_len, unsigned dst_ofs,
+ unsigned int n_bits)
+{
+ uint8_t *dst = dst_;
+
+ if (!n_bits) {
+ return;
+ }
+
+ dst += dst_len - (dst_ofs / 8 + 1);
+ dst_ofs %= 8;
+
+ if (dst_ofs) {
+ unsigned int chunk = MIN(n_bits, 8 - dst_ofs);
+
+ *dst &= ~(((1 << chunk) - 1) << dst_ofs);
+
+ n_bits -= chunk;
+ if (!n_bits) {
+ return;
+ }
+
+ dst--;
+ }
+
+ while (n_bits >= 8) {
+ *dst-- = 0;
+ n_bits -= 8;
+ }
+
+ if (n_bits) {
+ *dst &= ~((1 << n_bits) - 1);
+ }
+}
+
/* 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. Bit 0 of
* 'dst' is the bit with value 1 in dst[dst_len - 1], bit 1 is the bit with
diff --git a/lib/util.h b/lib/util.h
index c8eb004..d504f2f 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
+ * Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira Networks.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
@@ -211,6 +211,8 @@ bool is_all_ones(const uint8_t *, size_t);
void bitwise_copy(const void *src, unsigned int src_len, unsigned int src_ofs,
void *dst, unsigned int dst_len, unsigned int dst_ofs,
unsigned int n_bits);
+void bitwise_zero(void *dst_, unsigned int dst_len, unsigned dst_ofs,
+ unsigned int n_bits);
void bitwise_put(uint64_t value,
void *dst, unsigned int dst_len, unsigned int dst_ofs,
unsigned int n_bits);
--
1.7.2.5
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