Use a simple run length encoding in xor_into_buf, so long blocks of spaces,

zero bytes, etc (relatively common, especially with the statistical
pollers that use xor_into_buf) are removed. Counters wrap at 256.

2 files changed, 22 insertions, 3 deletions

diff --git a/src/utils/xor_buf.cpp b/src/utils/xor_buf.cpp
index df4e62db9..779be81c3 100644
--- a/src/utils/xor_buf.cpp
+++ b/src/utils/xor_buf.cpp
@@ -16,11 +16,28 @@ u32bit xor_into_buf(byte buf[], u32bit buf_i, u32bit length,
    {
    const byte* in = static_cast<const byte*>(in_void);
 
+   byte last = 0;
+   byte count = 0;
+
    for(u32bit i = 0; i != in_len; ++i)
       {
-      buf[buf_i] ^= in[i];
-      buf_i = (buf_i + 1) % length;
+      if(in[i] != last)
+         {
+         buf[buf_i] ^= last;
+         buf_i = (buf_i + 1) % length;
+
+         buf[buf_i] ^= count;
+         buf_i = (buf_i + 1) % length;
+
+         last = in[i];
+         count = 1;
+         }
+      else
+         ++count;
       }
+
+   // final values of last, count are thrown away
+
    return buf_i;
    }
 
diff --git a/src/utils/xor_buf.h b/src/utils/xor_buf.h
index 74bfeef0b..076877e02 100644
--- a/src/utils/xor_buf.h
+++ b/src/utils/xor_buf.h
@@ -68,7 +68,9 @@ inline void xor_buf(byte out[],
    }
 
 /**
-* XOR values into buffer. Might do RLE on input
+* XOR values into buffer. Uses RLE compression
+* Intended for use in entropy sources to gather collected
+* data into a buffer to pass to an RNG.
 */
 u32bit xor_into_buf(byte buf[], u32bit buf_i, u32bit length,
                     const void* in_void, u32bit in_len);