Benchmark Contest:Count character ratio in DNA file

RULES:
The program must count(without prior knowledge of file beyond its format) GC-content of source file.
GC-content is fraction of GC vs AT chars found in the file expressed as floating point number. http://en.wikipedia.org/wiki/GC-content
source file https://github.com/dubst3pp4/GC-Content-OOC/blob/master/Homo_sapiens.GRCh37.67.dna_rm.chromosome.Y.fa

>>7
12.7 cycles/byte is not impressive at all.