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Posted to commits@harmony.apache.org by "Chunrong Lai (JIRA)" <ji...@apache.org> on 2009/02/25 17:51:01 UTC
[jira] Commented: (HARMONY-5901) [drlvm][jit]integer MUL, DIV and
REM strength reduction
[ https://issues.apache.org/jira/browse/HARMONY-5901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12676700#action_12676700 ]
Chunrong Lai commented on HARMONY-5901:
---------------------------------------
Committed in r747857. Xiaoming, please help to verify it.
> [drlvm][jit]integer MUL, DIV and REM strength reduction
> -------------------------------------------------------
>
> Key: HARMONY-5901
> URL: https://issues.apache.org/jira/browse/HARMONY-5901
> Project: Harmony
> Issue Type: Improvement
> Components: DRLVM
> Reporter: Xiaoming Gu
> Assignee: Chunrong Lai
> Attachments: 5901.patch, H5901-V2.patch, H5901-V3.patch, H5901-V4.patch, H5901-V5.patch, H5901-V6.patch, H5901-V7.patch, H5901-V8.patch, H5901-V9.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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