[Mono-dev] implementation of BitConverter [possible perf improvements?]
jonathan.shore at gmail.com
Thu Nov 17 23:44:35 EST 2011
I was looking at the code for the mono implementation of BitConverter and was surprised to see that common types (such as long) are converted by writing to a byte* a byte at a time. I don't know why it was done this way unless this was done to avoid a temporary pin of the byte.
The current code is:
unsafe static void PutBytes (byte *dst, byte src, int start_index, int count)
if (src == null)
throw new ArgumentNullException ("value");
if (start_index < 0 || (start_index > src.Length - 1))
throw new ArgumentOutOfRangeException ("startIndex", "Index was"
+ " out of range. Must be non-negative and less than the"
+ " size of the collection.");
// avoid integer overflow (with large pos/neg start_index values)
if (src.Length - count < start_index)
throw new ArgumentException ("Destination array is not long"
+ " enough to copy all the items in the collection."
+ " Check array index and length.");
for (int i = 0; i < count; i++)
dst[i] = src[i + start_index];
unsafe public static long ToInt64 (byte value, int startIndex)
PutBytes ((byte *) &ret, value, startIndex, 8);
The above code does avoid pinning the byte buffer, however is 3-4x slower than, say doing this:
unsafe public static long ToLong (byte buffer, int offset)
fixed (byte* pbuf = buffer)
long* vlong = (long*)(pbuf + offset);
Any reason why we would not want to do the above?
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