[ https://issues.apache.org/jira/browse/HARMONY-5901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12619805#action_12619805 ] Aleksey Shipilev commented on HARMONY-5901: ------------------------------------------- That's good, Xiaoming! A couple of little "polishing" comments: a. eliminate "&& true" from if conditions, that was introduced by me for debugging purposes and I forgot to sweep them out b. move out common blocks from switch cases After that the patch can be committed, if it passes VM/Classlib tests. > 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, H5901-V2.patch, H5901-V3.patch, H5901-V4.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. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.