Hello, I created a formal webrev:
Issue: https://bugs.openjdk.java.net/browse/JDK-8057793 Webrev: http://cr.openjdk.java.net/~bpb/8057793/webrev.00/ Based on manual inspection of the revised code the patch looks good to me. The test submitted with the issue now succeeds as do all regression tests in jdk/test/java/math to which I also added the code from the test case in the issue report. Note that this webrev is with respect to JDK 9. Thanks, Brian On Sep 11, 2014, at 6:35 PM, Joe Darcy <joe.da...@oracle.com> wrote: > Hello, > > Hmmm. I haven't dived into the details of the code, but setScale calls out to > divide functionality so it is plausible a bug in divide could cause a problem > in setScale. > > Thanks for the bug report, > > -Joe > > On 9/9/2014 1:30 AM, Robert Gibson wrote: >> >> >> Hi there, >> >> I came across a case in BigDecimal division where the dividend ends up >> getting mutated, which is rather strange for a seemingly immutable class! >> (It's a subset of the cases where the Burnikel-Ziegler algorithm is used, I >> haven't done the analysis to find out under which exact conditions it's >> triggered.) >> >> The attached patch - against the JDK8 version - should fix the problem, at >> the cost of an extra array copy. Could somebody review and/or comment >> please? >> >> Thanks, >> Robert >> >> --- MutableBigInteger.java 2014-09-04 09:42:23.426815000 +0200 >> +++ MutableBigInteger.java.patched 2014-09-04 09:46:21.344132000 +0200 >> @@ -1261,19 +1261,20 @@ >> int sigma = (int) Math.max(0, n32 - b.bitLength()); // step >> 3: sigma = max{T | (2^T)*B < beta^n} >> MutableBigInteger bShifted = new MutableBigInteger(b); >> bShifted.safeLeftShift(sigma); // step 4a: shift b so its >> length is a multiple of n >> - safeLeftShift(sigma); // step 4b: shift this by the same >> amount >> + MutableBigInteger aShifted = new MutableBigInteger (this); >> + aShifted.safeLeftShift(sigma); // step 4b: shift a by the >> same amount >> - // step 5: t is the number of blocks needed to accommodate this >> plus one additional bit >> - int t = (int) ((bitLength()+n32) / n32); >> + // step 5: t is the number of blocks needed to accommodate a >> plus one additional bit >> + int t = (int) ((aShifted.bitLength()+n32) / n32); >> if (t < 2) { >> t = 2; >> } >> - // step 6: conceptually split this into blocks a[t-1], ..., a[0] >> - MutableBigInteger a1 = getBlock(t-1, t, n); // the most >> significant block of this >> + // step 6: conceptually split a into blocks a[t-1], ..., a[0] >> + MutableBigInteger a1 = aShifted.getBlock(t-1, t, n); // the >> most significant block of a >> // step 7: z[t-2] = [a[t-1], a[t-2]] >> - MutableBigInteger z = getBlock(t-2, t, n); // the second to >> most significant block >> + MutableBigInteger z = aShifted.getBlock(t-2, t, n); // the >> second to most significant block >> z.addDisjoint(a1, n); // z[t-2] >> // do schoolbook division on blocks, dividing 2-block numbers >> by 1-block numbers >> @@ -1284,7 +1285,7 @@ >> ri = z.divide2n1n(bShifted, qi); >> // step 8b: z = [ri, a[i-1]] >> - z = getBlock(i-1, t, n); // a[i-1] >> + z = aShifted.getBlock(i-1, t, n); // a[i-1] >> z.addDisjoint(ri, n); >> quotient.addShifted(qi, i*n); // update q (part of step 9) >> } >> @@ -1292,7 +1293,7 @@ >> ri = z.divide2n1n(bShifted, qi); >> quotient.add(qi); >> - ri.rightShift(sigma); // step 9: this and b were shifted, so >> shift back >> + ri.rightShift(sigma); // step 9: a and b were shifted, so >> shift back >> return ri; >> } >> } >
