harmony-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Xiaoming Gu (JIRA)" <j...@apache.org>
Subject [jira] Created: (HARMONY-5901) replace integer multiplication or division with shift if one of multipliers or divisor is a power of 2
Date Tue, 08 Jul 2008 06:50:36 GMT
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


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.


Mime
View raw message