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-rwxr-xr-xlib/crypto/RollingChecksum.cpp28
1 files changed, 26 insertions, 2 deletions
diff --git a/lib/crypto/RollingChecksum.cpp b/lib/crypto/RollingChecksum.cpp
index 75bad7df..a2954e3a 100755
--- a/lib/crypto/RollingChecksum.cpp
+++ b/lib/crypto/RollingChecksum.cpp
@@ -20,11 +20,11 @@
// Created: 6/12/03
//
// --------------------------------------------------------------------------
-RollingChecksum::RollingChecksum(const void *data, unsigned int Length)
+RollingChecksum::RollingChecksum(const void * const data, const unsigned int Length)
: a(0),
b(0)
{
- uint8_t *block = (uint8_t *)data;
+ const uint8_t *block = (const uint8_t *)data;
for(unsigned int x = Length; x >= 1; --x)
{
a += (*block);
@@ -34,5 +34,29 @@ RollingChecksum::RollingChecksum(const void *data, unsigned int Length)
}
}
+// --------------------------------------------------------------------------
+//
+// Function
+// Name: RollingChecksum::RollForwardSeveral(uint8_t*, uint8_t*, unsigned int, unsigned int)
+// Purpose: Move the checksum forward a block, given a pointer to the first byte of the current block,
+// and a pointer just after the last byte of the current block and the length of the block and of the skip.
+// Created: 7/14/05
+//
+// --------------------------------------------------------------------------
+void RollingChecksum::RollForwardSeveral(const uint8_t * const StartOfThisBlock, const uint8_t * const LastOfNextBlock, const unsigned int Length, const unsigned int Skip)
+{
+ // IMPLEMENTATION NOTE: Everything is implicitly mod 2^16 -- uint16_t's will overflow nicely.
+ unsigned int i;
+ uint16_t sumBegin=0, j,k;
+ for(i=0; i < Skip; i++)
+ {
+ j = StartOfThisBlock[i];
+ k = LastOfNextBlock[i];
+ sumBegin += j;
+ a += (k - j);
+ b += a;
+ }
+ b -= Length * sumBegin;
+}