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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 | |
| 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
| -rw-r--r-- | apps/codecs/demac/libdemac/udiv32_arm.S | 10 | ||||
| -rw-r--r-- | firmware/target/arm/support-arm.S | 4 |
2 files changed, 9 insertions, 5 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: | |||
| 234 | mul \inv, \divisor, \neg | 234 | mul \inv, \divisor, \neg |
| 235 | smlawt \divisor, \divisor, \inv, \divisor | 235 | smlawt \divisor, \divisor, \inv, \divisor |
| 236 | mul \inv, \divisor, \neg | 236 | mul \inv, \divisor, \neg |
| 237 | /* This will save a cycle on ARMv6, but does not produce a correct result | 237 | /* This will save a cycle on ARMv6, but requires that the numerator sign |
| 238 | if numerator sign bit is set. This case accounts for about 1 in 10^7 of | 238 | bit is not set (that of inv is guaranteed unset). The branch should |
| 239 | divisions, done by the APE decoder, so we specialize for the more common | 239 | predict very well, making it typically 1 cycle, and thus both the branch |
| 240 | case and handle the uncommon large-numerator separately */ | 240 | and test fill delay cycles for the multiplies. Based on logging of |
| 241 | numerator sizes in the APE codec, the branch is taken about 1/10^7 of | ||
| 242 | the time. */ | ||
| 241 | #if ARM_ARCH >= 6 | 243 | #if ARM_ARCH >= 6 |
| 242 | tst \numerator, \numerator | 244 | tst \numerator, \numerator |
| 243 | smmla \divisor, \divisor, \inv, \divisor | 245 | smmla \divisor, \divisor, \inv, \divisor |
diff --git a/firmware/target/arm/support-arm.S b/firmware/target/arm/support-arm.S index dd17e0f5f7..b4577f6e9b 100644 --- a/firmware/target/arm/support-arm.S +++ b/firmware/target/arm/support-arm.S | |||
| @@ -244,7 +244,9 @@ | |||
| 244 | tst \numerator, \numerator | 244 | tst \numerator, \numerator |
| 245 | smmla \divisor, \divisor, \inv, \divisor | 245 | smmla \divisor, \divisor, \inv, \divisor |
| 246 | /* Branch to large-numerator handler, or else use smmul if sign bit is not | 246 | /* Branch to large-numerator handler, or else use smmul if sign bit is not |
| 247 | set. */ | 247 | set. This wins on average with random numerators, and should be no |
| 248 | slower than using umull for small numerator, even if prediction fails. | ||
| 249 | */ | ||
| 248 | bmi 40f | 250 | bmi 40f |
| 249 | smmul \inv, \numerator, \divisor | 251 | smmul \inv, \numerator, \divisor |
| 250 | #else | 252 | #else |