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| author | Andrew Mahone <andrew.mahone@gmail.com> | 2010-02-20 06:29:23 +0000 |
|---|---|---|
| committer | Andrew Mahone <andrew.mahone@gmail.com> | 2010-02-20 06:29:23 +0000 |
| commit | 950b2dfa2c42e6d8e0d1af546efb9368d5b89dc3 (patch) | |
| tree | 992c34a5a572cf1a3ede22849a64c8e2f3405091 /apps | |
| parent | 3716abba9274f544dd31cdf4e6c83a845bf2a801 (diff) | |
| download | rockbox-950b2dfa2c42e6d8e0d1af546efb9368d5b89dc3.tar.gz rockbox-950b2dfa2c42e6d8e0d1af546efb9368d5b89dc3.zip | |
Clarify comments in ARMv6 divider regarding special-case handling of large (high bit set) numerators.
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@24783 a1c6a512-1295-4272-9138-f99709370657
Diffstat (limited to 'apps')
| -rw-r--r-- | apps/codecs/demac/libdemac/udiv32_arm.S | 10 |
1 files changed, 6 insertions, 4 deletions
diff --git a/apps/codecs/demac/libdemac/udiv32_arm.S b/apps/codecs/demac/libdemac/udiv32_arm.S index 939fce17d4..10c0731db1 100644 --- a/apps/codecs/demac/libdemac/udiv32_arm.S +++ b/apps/codecs/demac/libdemac/udiv32_arm.S @@ -234,10 +234,12 @@ udiv32_arm: mul \inv, \divisor, \neg smlawt \divisor, \divisor, \inv, \divisor mul \inv, \divisor, \neg - /* This will save a cycle on ARMv6, but does not produce a correct result - if numerator sign bit is set. This case accounts for about 1 in 10^7 of - divisions, done by the APE decoder, so we specialize for the more common - case and handle the uncommon large-numerator separately */ + /* This will save a cycle on ARMv6, but requires that the numerator sign + bit is not set (that of inv is guaranteed unset). The branch should + predict very well, making it typically 1 cycle, and thus both the branch + and test fill delay cycles for the multiplies. Based on logging of + numerator sizes in the APE codec, the branch is taken about 1/10^7 of + the time. */ #if ARM_ARCH >= 6 tst \numerator, \numerator smmla \divisor, \divisor, \inv, \divisor |