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added O(n^1.5) BigDecimal parser implementation (#677)
Co-authored-by: Ferenc Csaky <[email protected]>
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src/main/java/com/fasterxml/jackson/core/io/BigDecimalParser.java
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package com.fasterxml.jackson.core.io; | ||
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import java.math.BigDecimal; | ||
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// Based on a great idea of Eric Obermühlner to use a tree of smaller BigDecimals for parsing really big numbers | ||
// with O(n^1.5) complexity instead of O(n^2) when using the constructor for a decimal representation from JDK 8/11: | ||
// https://github.com/eobermuhlner/big-math/commit/7a5419aac8b2adba2aa700ccf00197f97b2ad89f | ||
public final class BigDecimalParser { | ||
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private final char[] chars; | ||
private final int off; | ||
private final int len; | ||
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BigDecimalParser(char[] chars, int off, int len) { | ||
this.chars = chars; | ||
this.off = off; | ||
this.len = len; | ||
} | ||
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BigDecimal parse() throws NumberFormatException { | ||
try { | ||
if (len < 500) { | ||
return new BigDecimal(chars, off, len); | ||
} | ||
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int splitLen = len / 10; | ||
return parseBigDecimal(splitLen); | ||
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} catch (NumberFormatException e) { | ||
String val = new String(chars, off, len); | ||
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throw new NumberFormatException("Value \"" + val + "\" can not be represented as BigDecimal." | ||
+ " Reason: " + e.getMessage()); | ||
} | ||
} | ||
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private BigDecimal parseBigDecimal(int splitLen) { | ||
boolean numHasSign = false; | ||
boolean expHasSign = false; | ||
boolean neg = false; | ||
int numIdx = 0; | ||
int expIdx = -1; | ||
int dotIdx = -1; | ||
int scale = 0; | ||
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for (int i = off; i < len; i++) { | ||
char c = chars[i]; | ||
switch (c) { | ||
case '+': | ||
if (expIdx >= 0) { | ||
if (expHasSign) { | ||
throw new NumberFormatException("Multiple signs in exponent"); | ||
} | ||
expHasSign = true; | ||
} else { | ||
if (numHasSign) { | ||
throw new NumberFormatException("Multiple signs in number"); | ||
} | ||
numHasSign = true; | ||
numIdx = i + 1; | ||
} | ||
break; | ||
case '-': | ||
if (expIdx >= 0) { | ||
if (expHasSign) { | ||
throw new NumberFormatException("Multiple signs in exponent"); | ||
} | ||
expHasSign = true; | ||
} else { | ||
if (numHasSign) { | ||
throw new NumberFormatException("Multiple signs in number"); | ||
} | ||
numHasSign = true; | ||
neg = true; | ||
numIdx = i + 1; | ||
} | ||
break; | ||
case 'e': | ||
case 'E': | ||
if (expIdx >= 0) { | ||
throw new NumberFormatException("Multiple exponent markers"); | ||
} | ||
expIdx = i; | ||
break; | ||
case '.': | ||
if (dotIdx >= 0) { | ||
throw new NumberFormatException("Multiple decimal points"); | ||
} | ||
dotIdx = i; | ||
break; | ||
default: | ||
if (dotIdx >= 0 && expIdx == -1) { | ||
scale++; | ||
} | ||
} | ||
} | ||
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int numEndIdx; | ||
int exp = 0; | ||
if (expIdx >= 0) { | ||
numEndIdx = expIdx; | ||
String expStr = new String(chars, expIdx + 1, len - expIdx - 1); | ||
exp = Integer.parseInt(expStr); | ||
scale = adjustScale(scale, exp); | ||
} else { | ||
numEndIdx = len; | ||
} | ||
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BigDecimal res; | ||
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if (dotIdx >= 0) { | ||
int leftLen = dotIdx - numIdx; | ||
BigDecimal left = toBigDecimalRec(numIdx, leftLen, exp, splitLen); | ||
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int rightLen = numEndIdx - dotIdx - 1; | ||
BigDecimal right = toBigDecimalRec(dotIdx + 1, rightLen, exp - rightLen, splitLen); | ||
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res = left.add(right); | ||
} else { | ||
res = toBigDecimalRec(numIdx, numEndIdx - numIdx, exp, splitLen); | ||
} | ||
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if (scale != 0) { | ||
res = res.setScale(scale); | ||
} | ||
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if (neg) { | ||
res = res.negate(); | ||
} | ||
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return res; | ||
} | ||
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private int adjustScale(int scale, long exp) { | ||
long adjScale = scale - exp; | ||
if (adjScale > Integer.MAX_VALUE || adjScale < Integer.MIN_VALUE) { | ||
throw new NumberFormatException( | ||
"Scale out of range: " + adjScale + " while adjusting scale " + scale + " to exponent " + exp); | ||
} | ||
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return (int) adjScale; | ||
} | ||
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private BigDecimal toBigDecimalRec(int off, int len, int scale, int splitLen) { | ||
if (len > splitLen) { | ||
int mid = len / 2; | ||
BigDecimal left = toBigDecimalRec(off, mid, scale + len - mid, splitLen); | ||
BigDecimal right = toBigDecimalRec(off + mid, len - mid, scale, splitLen); | ||
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return left.add(right); | ||
} | ||
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return len == 0 ? BigDecimal.ZERO : new BigDecimal(chars, off, len).movePointRight(scale); | ||
} | ||
} |
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