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Date: Tue, 8 Jul 2008 06:38:58 -0700 (PDT)
From: "Aleksey Shipilev (JIRA)" <jira@apache.org>
To: commits@harmony.apache.org
Subject: [jira] Commented: (HARMONY-5901) replace integer multiplication or
 division with shift if one of multipliers or divisor is a power of 2
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    [ https://issues.apache.org/jira/browse/HARMONY-5901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12611582#action_12611582 ] 

Aleksey Shipilev commented on HARMONY-5901:
-------------------------------------------

There's really the bug in the patch.
You should handle the divOp when remainder is requested, see corresponding boolean parameter in argument list.

> 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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