src/java.base/share/classes/java/math/MutableBigInteger.java

Print this page
rev 10641 : 8057793: BigDecimal is no longer effectively immutable
Summary: Modify MutableBigInteger.divideAndRemainderBurnikelZiegler() to copy the instance (this) to a new MutableBigInteger to use as the dividend.
Reviewed-by: TBD
Contributed-by: robbiexgibson@yahoo.com

*** 1259,1300 **** int n = j * m; // step 2b: block length in 32-bit units long n32 = 32L * n; // block length in bits 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 ! // step 5: t is the number of blocks needed to accommodate this plus one additional bit ! int t = (int) ((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 7: z[t-2] = [a[t-1], a[t-2]] ! MutableBigInteger z = 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 MutableBigInteger qi = new MutableBigInteger(); MutableBigInteger ri; for (int i=t-2; i > 0; i--) { // step 8a: compute (qi,ri) such that z=b*qi+ri ri = z.divide2n1n(bShifted, qi); // step 8b: z = [ri, a[i-1]] ! z = getBlock(i-1, t, n); // a[i-1] z.addDisjoint(ri, n); quotient.addShifted(qi, i*n); // update q (part of step 9) } // final iteration of step 8: do the loop one more time for i=0 but leave z unchanged ri = z.divide2n1n(bShifted, qi); quotient.add(qi); ! ri.rightShift(sigma); // step 9: this and b were shifted, so shift back return ri; } } /** --- 1259,1301 ---- int n = j * m; // step 2b: block length in 32-bit units long n32 = 32L * n; // block length in bits 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 ! 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 a plus one additional bit ! int t = (int) ((aShifted.bitLength()+n32) / n32); if (t < 2) { t = 2; } ! // 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 = 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 MutableBigInteger qi = new MutableBigInteger(); MutableBigInteger ri; for (int i=t-2; i > 0; i--) { // step 8a: compute (qi,ri) such that z=b*qi+ri ri = z.divide2n1n(bShifted, qi); // step 8b: z = [ri, 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) } // final iteration of step 8: do the loop one more time for i=0 but leave z unchanged ri = z.divide2n1n(bShifted, qi); quotient.add(qi); ! ri.rightShift(sigma); // step 9: a and b were shifted, so shift back return ri; } } /**