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Replace unsigned with signed integer arithmetic in strtod

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abolz 2018-06-15 10:38:21 +02:00
parent 29b6c9b7dc
commit c59ecc857d
1 changed files with 32 additions and 27 deletions
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59
include/rapidjson/internal/strtod.h
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@ -126,20 +126,20 @@ inline bool StrtodFast(double d, int p, double* result) {
} }
// Compute an approximation and see if it is within 1/2 ULP // Compute an approximation and see if it is within 1/2 ULP
inline bool StrtodDiyFp(const char* decimals, size_t length, size_t decimalPosition, int exp, double* result) { inline bool StrtodDiyFp(const char* decimals, int dLen, int dExp, double* result) {
uint64_t significand = 0; uint64_t significand = 0;
size_t i = 0; // 2^64 - 1 = 18446744073709551615, 1844674407370955161 = 0x1999999999999999 int i = 0; // 2^64 - 1 = 18446744073709551615, 1844674407370955161 = 0x1999999999999999
for (; i < length; i++) { for (; i < dLen; i++) {
if (significand > RAPIDJSON_UINT64_C2(0x19999999, 0x99999999) || if (significand > RAPIDJSON_UINT64_C2(0x19999999, 0x99999999) ||
(significand == RAPIDJSON_UINT64_C2(0x19999999, 0x99999999) && decimals[i] > '5')) (significand == RAPIDJSON_UINT64_C2(0x19999999, 0x99999999) && decimals[i] > '5'))
break; break;
significand = significand * 10u + static_cast<unsigned>(decimals[i] - '0'); significand = significand * 10u + static_cast<unsigned>(decimals[i] - '0');
} }
if (i < length && decimals[i] >= '5') // Rounding if (i < dLen && decimals[i] >= '5') // Rounding
significand++; significand++;
size_t remaining = length - i; int remaining = dLen - i;
const int kUlpShift = 3; const int kUlpShift = 3;
const int kUlp = 1 << kUlpShift; const int kUlp = 1 << kUlpShift;
int64_t error = (remaining == 0) ? 0 : kUlp / 2; int64_t error = (remaining == 0) ? 0 : kUlp / 2;
@ -148,7 +148,7 @@ inline bool StrtodDiyFp(const char* decimals, size_t length, size_t decimalPosit
v = v.Normalize(); v = v.Normalize();
error <<= -v.e; error <<= -v.e;
const int dExp = static_cast<int>(decimalPosition) - static_cast<int>(i) + exp; dExp += remaining;
int actualExp; int actualExp;
DiyFp cachedPower = GetCachedPower10(dExp, &actualExp); DiyFp cachedPower = GetCachedPower10(dExp, &actualExp);
@ -165,7 +165,7 @@ inline bool StrtodDiyFp(const char* decimals, size_t length, size_t decimalPosit
int adjustment = dExp - actualExp - 1; int adjustment = dExp - actualExp - 1;
RAPIDJSON_ASSERT(adjustment >= 0 && adjustment < 7); RAPIDJSON_ASSERT(adjustment >= 0 && adjustment < 7);
v = v * kPow10[adjustment]; v = v * kPow10[adjustment];
if (length + static_cast<unsigned>(adjustment)> 19u) // has more digits than decimal digits in 64-bit if (dLen + static_cast<unsigned>(adjustment)> 19u) // has more digits than decimal digits in 64-bit
error += kUlp / 2; error += kUlp / 2;
} }
@ -203,9 +203,8 @@ inline bool StrtodDiyFp(const char* decimals, size_t length, size_t decimalPosit
return halfWay - static_cast<unsigned>(error) >= precisionBits || precisionBits >= halfWay + static_cast<unsigned>(error); return halfWay - static_cast<unsigned>(error) >= precisionBits || precisionBits >= halfWay + static_cast<unsigned>(error);
} }
inline double StrtodBigInteger(double approx, const char* decimals, size_t length, size_t decimalPosition, int exp) { inline double StrtodBigInteger(double approx, const char* decimals, int length, int dExp) {
const BigInteger dInt(decimals, length); const BigInteger dInt(decimals, length);
const int dExp = static_cast<int>(decimalPosition) - static_cast<int>(length) + exp;
Double a(approx); Double a(approx);
int cmp = CheckWithinHalfULP(a.Value(), dInt, dExp); int cmp = CheckWithinHalfULP(a.Value(), dInt, dExp);
if (cmp < 0) if (cmp < 0)
@ -229,41 +228,47 @@ inline double StrtodFullPrecision(double d, int p, const char* decimals, size_t
if (StrtodFast(d, p, &result)) if (StrtodFast(d, p, &result))
return result; return result;
RAPIDJSON_ASSERT(length <= INT_MAX);
int dLen = static_cast<int>(length);
RAPIDJSON_ASSERT(length >= decimalPosition);
RAPIDJSON_ASSERT(length - decimalPosition <= INT_MAX);
int dExpAdjust = static_cast<int>(length - decimalPosition);
RAPIDJSON_ASSERT(exp >= INT_MIN + dExpAdjust);
int dExp = exp - dExpAdjust;
// Make sure length+dExp does not overflow
RAPIDJSON_ASSERT(dExp <= INT_MAX - dLen);
// Trim leading zeros // Trim leading zeros
while (*decimals == '0' && length > 1) { while (*decimals == '0' && dLen > 1) {
length--; dLen--;
decimals++; decimals++;
RAPIDJSON_ASSERT(decimalPosition > 0);
decimalPosition--;
} }
// Trim trailing zeros // Trim trailing zeros
while (decimals[length - 1] == '0' && length > 1) { while (decimals[dLen - 1] == '0' && dLen > 1) {
length--; dLen--;
RAPIDJSON_ASSERT(decimalPosition > 0); dExp++;
decimalPosition--;
exp++;
} }
// Trim right-most digits // Trim right-most digits
const int kMaxDecimalDigit = 780; const int kMaxDecimalDigit = 780;
if (static_cast<int>(length) > kMaxDecimalDigit) { if (dLen > kMaxDecimalDigit) {
int delta = (static_cast<int>(length) - kMaxDecimalDigit); dExp += dLen - kMaxDecimalDigit;
exp += delta; dLen = kMaxDecimalDigit;
RAPIDJSON_ASSERT(decimalPosition > static_cast<unsigned>(delta));
decimalPosition -= static_cast<unsigned>(delta);
length = kMaxDecimalDigit;
} }
// If too small, underflow to zero // If too small, underflow to zero
if (int(length) + exp < -324) if (dLen + dExp < -324)
return 0.0; return 0.0;
if (StrtodDiyFp(decimals, length, decimalPosition, exp, &result)) if (StrtodDiyFp(decimals, dLen, dExp, &result))
return result; return result;
// Use approximation from StrtodDiyFp and make adjustment with BigInteger comparison // Use approximation from StrtodDiyFp and make adjustment with BigInteger comparison
return StrtodBigInteger(result, decimals, length, decimalPosition, exp); return StrtodBigInteger(result, decimals, dLen, dExp);
} }
} // namespace internal } // namespace internal