Simplify forward-WHT + SSE2 version

no precision loss observed
speed is not really faster (0.5% at max), as forward-WHT isn't called often.

also: replaced a "int << 3" (undefined by C-spec) by a "int * 8"
( supersedes https://gerrit.chromium.org/gerrit/#/c/48739/ )

Change-Id: I2d980ec2f20f4ff6be5636105ff4f1c70ffde401
3 files changed