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improved BigDecimal parsing performance #3992

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37 changes: 14 additions & 23 deletions core/src/main/java/com/alibaba/fastjson2/JSONReaderUTF16.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4379,18 +4379,12 @@ public final BigDecimal readBigDecimal() {
}

valueType = JSON_TYPE_INT;
boolean overflow = false;
int digitCount = 0; // Total digit count for overflow detection
long longValue = 0;
while (ch >= '0' && ch <= '9') {
valid = true;
if (!overflow) {
long r = longValue * 10;
if ((longValue | 10) >>> 31 == 0L || (r / 10 == longValue)) {
longValue = r + (ch - '0');
} else {
overflow = true;
}
}
longValue = (longValue << 3) + (longValue << 1) + (ch & 0xf);
digitCount++;

if (offset == end) {
ch = EOI;
Expand All @@ -4400,25 +4394,15 @@ public final BigDecimal readBigDecimal() {
ch = chars[offset++];
}

if (longValue < 0) {
overflow = true;
}

this.scale = 0;
if (ch == '.') {
valueType = JSON_TYPE_DEC;
ch = chars[offset++];
while (ch >= '0' && ch <= '9') {
valid = true;
this.scale++;
if (!overflow) {
long r = longValue * 10;
if ((longValue | 10) >>> 31 == 0L || (r / 10 == longValue)) {
longValue = r + (ch - '0');
} else {
overflow = true;
}
}
longValue = (longValue << 3) + (longValue << 1) + (ch & 0xf);
digitCount++;

if (offset == end) {
ch = EOI;
Expand All @@ -4429,6 +4413,9 @@ public final BigDecimal readBigDecimal() {
}
}

// Check overflow: more than 18 digits, or 19 digits with negative value (sign bit set)
boolean overflow = digitCount > 18 && (digitCount > 19 || longValue < 0);

int expValue = 0;
if (ch == 'e' || ch == 'E') {
boolean negativeExp;
Expand Down Expand Up @@ -4520,8 +4507,12 @@ public final BigDecimal readBigDecimal() {
}
}
if (!value) {
if (expValue == 0 && !overflow && longValue != 0) {
decimal = BigDecimal.valueOf(negative ? -longValue : longValue, scale);
if (!overflow && longValue != 0) {
// Combine scale and exponent: scale - expValue
// For 1.5E3: scale=1, exp=3 => combined=-2 => 1500
// For 1.5E-3: scale=1, exp=-3 => combined=4 => 0.0015
int combinedScale = scale - expValue;
decimal = BigDecimal.valueOf(negative ? -longValue : longValue, combinedScale);
value = true;
}

Expand Down
37 changes: 14 additions & 23 deletions core/src/main/java/com/alibaba/fastjson2/JSONReaderUTF8.java
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Original file line number Diff line number Diff line change
Expand Up @@ -6822,18 +6822,12 @@ public final BigDecimal readBigDecimal() {
}

valueType = JSON_TYPE_INT;
boolean overflow = false;
int digitCount = 0; // Total digit count for overflow detection
long longValue = 0;
while (ch >= '0' && ch <= '9') {
valid = true;
if (!overflow) {
long r = longValue * 10;
if ((longValue | 10) >>> 31 == 0L || (r / 10 == longValue)) {
longValue = r + (ch - '0');
} else {
overflow = true;
}
}
longValue = (longValue << 3) + (longValue << 1) + (ch & 0xf);
digitCount++;

if (offset == end) {
ch = EOI;
Expand All @@ -6843,25 +6837,15 @@ public final BigDecimal readBigDecimal() {
ch = bytes[offset++];
}

if (longValue < 0) {
overflow = true;
}

this.scale = 0;
if (ch == '.') {
valueType = JSON_TYPE_DEC;
ch = bytes[offset++];
while (ch >= '0' && ch <= '9') {
valid = true;
this.scale++;
if (!overflow) {
long r = longValue * 10;
if ((longValue | 10) >>> 31 == 0L || (r / 10 == longValue)) {
longValue = r + (ch - '0');
} else {
overflow = true;
}
}
longValue = (longValue << 3) + (longValue << 1) + (ch & 0xf);
digitCount++;

if (offset == end) {
ch = EOI;
Expand All @@ -6872,6 +6856,9 @@ public final BigDecimal readBigDecimal() {
}
}

// Check overflow: more than 18 digits, or 19 digits with negative value (sign bit set)

@wenshao wenshao Apr 25, 2026

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[Critical] This post-loop overflow check can accept corrupted 19-digit values. For exactly 19 digits, values greater than Long.MAX_VALUE may overflow during longValue = longValue * 10 + digit and still finish with a non-negative wrapped longValue, so they take the BigDecimal.valueOf(longValue, combinedScale) fast path instead of falling back to TypeUtils.parseBigDecimal(...). That can silently return the wrong BigDecimal for valid JSON numbers outside signed long range.

A safer fix is to restore per-digit overflow detection, or add an exact 19-digit range check before using the accumulated longValue; otherwise force the existing string-based fallback.

— gpt-5.5 via Qwen Code /review

boolean overflow = digitCount > 18 && (digitCount > 19 || longValue < 0);

int expValue = 0;
if (ch == 'e' || ch == 'E') {
boolean negativeExp;
Expand Down Expand Up @@ -6959,8 +6946,12 @@ public final BigDecimal readBigDecimal() {
}
}
if (!value) {
if (expValue == 0 && !overflow && longValue != 0) {
decimal = BigDecimal.valueOf(negative ? -longValue : longValue, scale);
if (!overflow && longValue != 0) {
// Combine scale and exponent: scale - expValue
// For 1.5E3: scale=1, exp=3 => combined=-2 => 1500
// For 1.5E-3: scale=1, exp=-3 => combined=4 => 0.0015
int combinedScale = scale - expValue;
decimal = BigDecimal.valueOf(negative ? -longValue : longValue, combinedScale);
value = true;
}

Expand Down
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