From d3f912c1f06b90960659d59bb75d2eb98932fde6 Mon Sep 17 00:00:00 2001 From: Michael Niedermayer Date: Sat, 4 Feb 2012 20:27:02 +0100 Subject: [PATCH] adler32: add comment for the SIMD code Signed-off-by: Michael Niedermayer --- libavutil/adler32.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/libavutil/adler32.c b/libavutil/adler32.c index c5f96db5e5..bc9b9a7e5a 100644 --- a/libavutil/adler32.c +++ b/libavutil/adler32.c @@ -57,6 +57,11 @@ unsigned long av_adler32_update(unsigned long adler, const uint8_t * buf, len2 -= 8; buf+=8; } + + //We combine the 8 interleaved adler32 checksums without overflows + //Decreasing the number of iterations would allow below code to be + //simplified but would likely be slower due to the fewer iterations + //of the inner loop s1 += ((a1+b1)*0x1000100010001)>>48; s2 += ((((a2&0xFFFF0000FFFF)+(b2&0xFFFF0000FFFF)+((a2>>16)&0xFFFF0000FFFF)+((b2>>16)&0xFFFF0000FFFF))*0x800000008)>>32) #if HAVE_BIGENDIAN