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Posted to commits@harmony.apache.org by "Aleksey Shipilev (JIRA)" <ji...@apache.org> on 2008/07/08 10:05:38 UTC
[jira] Commented: (HARMONY-5901) replace integer multiplication or
division with shift if one of multipliers or divisor is a power of 2
[ https://issues.apache.org/jira/browse/HARMONY-5901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12611479#action_12611479 ]
Aleksey Shipilev commented on HARMONY-5901:
-------------------------------------------
Good work, Xiaoming, but you need to clean up the patch a bit:
a. fold I4/I8 branches - set the optype in switch and proceed to common code block
b. replace <TAB>s with 4 spaces
> replace integer multiplication or division with shift if one of multipliers or divisor is a power of 2
> ------------------------------------------------------------------------------------------------------
>
> Key: HARMONY-5901
> URL: https://issues.apache.org/jira/browse/HARMONY-5901
> Project: Harmony
> Issue Type: Improvement
> Components: DRLVM
> Reporter: Xiaoming Gu
> Attachments: 5901.patch
>
>
> 1. Mulitiplication replacement
> a. It's about integer multiplication.
> b. One of two multipliers is a power of 2.
> c. The power of 2 could be negative.
> For example, 23*4 is transformed to 23<<2 and 23*(-4) is transformed to (23<<2)*(-1).
> 2. Division replacement
> a. It's about integer division.
> b. The divisor is a power of 2.
> c. The power of 2 could be negative.
> d. Because of round-up difference between division and shift right, the following equations from Aleksey are used.
> Baseline: q = a / (1 << d);
> Optimized: q = (a + [(1 << d) - 1] & (a >> 31)) >> d;
> For example, 23/4 is transformed to (23+((1<<2)-1)&(23>>31))>>2. and (-23)/(-4) is transformed to ((-23+((1<<2)-1)&(-23>>31))>>2)*(-1).
> 3. Comments for SAR and SHR swapped
> The comments for the two similar operations were misplaced in working_vm/vm/port/src/encoder/ia32_em64t.
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