2187 // approx = 0.5 * (approx + fraction / approx)
2188 approx = ONE_HALF.multiply(approx.add(working.divide(approx, mcTmp), mcTmp));
2189 guessPrecision *= 2;
2190 } while (guessPrecision < targetPrecision + 2);
2191
2192 BigDecimal result;
2193 RoundingMode targetRm = mc.getRoundingMode();
2194 if (targetRm == RoundingMode.UNNECESSARY || originalPrecision == 0) {
2195 RoundingMode tmpRm =
2196 (targetRm == RoundingMode.UNNECESSARY) ? RoundingMode.DOWN : targetRm;
2197 MathContext mcTmp = new MathContext(targetPrecision, tmpRm);
2198 result = approx.scaleByPowerOfTen(-scaleAdjust/2).round(mcTmp);
2199
2200 // If result*result != this numerically, the square
2201 // root isn't exact
2202 if (this.subtract(result.multiply(result)).compareTo(ZERO) != 0) {
2203 throw new ArithmeticException("Computed square root not exact.");
2204 }
2205 } else {
2206 result = approx.scaleByPowerOfTen(-scaleAdjust/2).round(mc);
2207 }
2208
2209 if (result.scale() != preferredScale) {
2210 // The preferred scale of an add is
2211 // max(addend.scale(), augend.scale()). Therefore, if
2212 // the scale of the result is first minimized using
2213 // stripTrailingZeros(), adding a zero of the
2214 // preferred scale rounding the correct precision will
2215 // perform the proper scale vs precision tradeoffs.
2216 result = result.stripTrailingZeros().
2217 add(zeroWithFinalPreferredScale,
2218 new MathContext(originalPrecision, RoundingMode.UNNECESSARY));
2219 }
2220 assert squareRootResultAssertions(result, mc);
2221 return result;
2222 } else {
2223 switch (signum) {
2224 case -1:
2225 throw new ArithmeticException("Attempted square root " +
2226 "of negative BigDecimal");
|
2187 // approx = 0.5 * (approx + fraction / approx)
2188 approx = ONE_HALF.multiply(approx.add(working.divide(approx, mcTmp), mcTmp));
2189 guessPrecision *= 2;
2190 } while (guessPrecision < targetPrecision + 2);
2191
2192 BigDecimal result;
2193 RoundingMode targetRm = mc.getRoundingMode();
2194 if (targetRm == RoundingMode.UNNECESSARY || originalPrecision == 0) {
2195 RoundingMode tmpRm =
2196 (targetRm == RoundingMode.UNNECESSARY) ? RoundingMode.DOWN : targetRm;
2197 MathContext mcTmp = new MathContext(targetPrecision, tmpRm);
2198 result = approx.scaleByPowerOfTen(-scaleAdjust/2).round(mcTmp);
2199
2200 // If result*result != this numerically, the square
2201 // root isn't exact
2202 if (this.subtract(result.multiply(result)).compareTo(ZERO) != 0) {
2203 throw new ArithmeticException("Computed square root not exact.");
2204 }
2205 } else {
2206 result = approx.scaleByPowerOfTen(-scaleAdjust/2).round(mc);
2207
2208 switch (targetRm) {
2209 case DOWN:
2210 case FLOOR:
2211 // Check if too big
2212 if (result.multiply(result).compareTo(this) > 0 ) {
2213 BigDecimal ulp = ulp = result.ulp();
2214 // Adjust increment down in case of 1.0 = 10^0
2215 // since the next smaller number is 1/10
2216 // closer than the next larger at exponent
2217 // boundaries.
2218 if (result.compareTo(ONE) == 0) {
2219 ulp = ulp.multiply(ONE_TENTH);
2220 }
2221 result = result.subtract(ulp);
2222 }
2223 break;
2224
2225 case UP:
2226 case CEILING:
2227 // Check if too small
2228 if (result.multiply(result).compareTo(this) < 0 ) {
2229 result = result.add(result.ulp());
2230 }
2231 break;
2232
2233 default:
2234 // Do nothing for half-way cases
2235 // HALF_DOWN, HALF_EVEN, HALF_UP
2236 // See fix-up in paper, up down by *1/2* ulp
2237 break;
2238 }
2239
2240 }
2241
2242 if (result.scale() != preferredScale) {
2243 // The preferred scale of an add is
2244 // max(addend.scale(), augend.scale()). Therefore, if
2245 // the scale of the result is first minimized using
2246 // stripTrailingZeros(), adding a zero of the
2247 // preferred scale rounding the correct precision will
2248 // perform the proper scale vs precision tradeoffs.
2249 result = result.stripTrailingZeros().
2250 add(zeroWithFinalPreferredScale,
2251 new MathContext(originalPrecision, RoundingMode.UNNECESSARY));
2252 }
2253 assert squareRootResultAssertions(result, mc);
2254 return result;
2255 } else {
2256 switch (signum) {
2257 case -1:
2258 throw new ArithmeticException("Attempted square root " +
2259 "of negative BigDecimal");
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