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Replaced the complex implementation of valueToString(double).
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The previous one was confusing and prone to buffer overflows, and didn't
work correctly with 16-decimal-digit numbers. The new one simply uses
snprintf with a standard format string.

The major change is that we don't always print a decimal point now.
Fortunately, JSON doesn't distinguish between integers and reals.
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@jacobsa
jacobsa committed Aug 8, 2013
1 parent bb53cd0 commit 32ffb93
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Showing 2 changed files with 23 additions and 44 deletions.
41 changes: 10 additions & 31 deletions src/lib_json/json_writer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -73,40 +73,19 @@ std::string valueToString( UInt value )

std::string valueToString( double value )
{
// Allocate a buffer that is more than large enough to store the 16 digits of
// precision requested below.
char buffer[32];

// Print into the buffer. We need not request the alternative representation
// that always has a decimal point because JSON doesn't distingish the
// concepts of reals and integers.
#if defined(_MSC_VER) && defined(__STDC_SECURE_LIB__) // Use secure version with visual studio 2005 to avoid warning.
sprintf_s(buffer, sizeof(buffer), "%#.16g", value);
#else
snprintf(buffer, sizeof(buffer), "%#.16g", value);
sprintf_s(buffer, sizeof(buffer), "%.16g", value);
#else
snprintf(buffer, sizeof(buffer), "%.16g", value);
#endif
char* ch = buffer + strlen(buffer) - 1;
if (*ch != '0') return buffer; // nothing to truncate, so save time
while(ch > buffer && *ch == '0'){
--ch;
}
char* last_nonzero = ch;
while(ch >= buffer){
switch(*ch){
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
--ch;
continue;
case '.':
// Truncate zeroes to save bytes in output, but keep one.
*(last_nonzero+2) = '\0';
return buffer;
default:
return buffer;
}
}

return buffer;
}

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26 changes: 13 additions & 13 deletions src/test_lib_json/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -462,7 +462,7 @@ JSONTEST_FIXTURE( ValueTest, integers )
JSONTEST_ASSERT_EQUAL(0.0, val.asDouble());
JSONTEST_ASSERT_EQUAL(0.0, val.asFloat());
JSONTEST_ASSERT_EQUAL(false, val.asBool());
JSONTEST_ASSERT_STRING_EQUAL("0.0", val.asString());
JSONTEST_ASSERT_STRING_EQUAL("0", val.asString());

// Zero (signed constructor arg)
val = Json::Value(0);
Expand Down Expand Up @@ -546,7 +546,7 @@ JSONTEST_FIXTURE( ValueTest, integers )
JSONTEST_ASSERT_EQUAL(0.0, val.asDouble());
JSONTEST_ASSERT_EQUAL(0.0, val.asFloat());
JSONTEST_ASSERT_EQUAL(false, val.asBool());
JSONTEST_ASSERT_STRING_EQUAL("0.0", val.asString());
JSONTEST_ASSERT_STRING_EQUAL("0", val.asString());

// 2^20 (signed constructor arg)
val = Json::Value(1 << 20);
Expand Down Expand Up @@ -629,7 +629,7 @@ JSONTEST_FIXTURE( ValueTest, integers )
JSONTEST_ASSERT_EQUAL((1 << 20), val.asDouble());
JSONTEST_ASSERT_EQUAL((1 << 20), val.asFloat());
JSONTEST_ASSERT_EQUAL(true, val.asBool());
JSONTEST_ASSERT_STRING_EQUAL("1048576.0", normalizeFloatingPointStr(val.asString()));
JSONTEST_ASSERT_STRING_EQUAL("1048576", normalizeFloatingPointStr(val.asString()));

// -2^20
val = Json::Value(-(1 << 20));
Expand Down Expand Up @@ -869,7 +869,7 @@ JSONTEST_FIXTURE( ValueTest, integers )
JSONTEST_ASSERT_EQUAL((Json::Int64(1) << 40), val.asDouble());
JSONTEST_ASSERT_EQUAL((Json::Int64(1) << 40), val.asFloat());
JSONTEST_ASSERT_EQUAL(true, val.asBool());
JSONTEST_ASSERT_STRING_EQUAL("1099511627776.0", normalizeFloatingPointStr(val.asString()));
JSONTEST_ASSERT_STRING_EQUAL("1099511627776", normalizeFloatingPointStr(val.asString()));

// -2^40
val = Json::Value(-(Json::Int64(1) << 40));
Expand Down Expand Up @@ -1035,7 +1035,7 @@ JSONTEST_FIXTURE( ValueTest, integers )
JSONTEST_ASSERT_EQUAL(1e19, val.asDouble());
JSONTEST_ASSERT_EQUAL(1e19, val.asFloat());
JSONTEST_ASSERT_EQUAL(true, val.asBool());
JSONTEST_ASSERT_STRING_EQUAL("1.000000000000000e+19", normalizeFloatingPointStr(val.asString()));
JSONTEST_ASSERT_STRING_EQUAL("1e+19", normalizeFloatingPointStr(val.asString()));

// uint64 max
val = Json::Value(Json::UInt64(kuint64max));
Expand Down Expand Up @@ -1114,7 +1114,7 @@ JSONTEST_FIXTURE( ValueTest, nonIntegers )
JSONTEST_ASSERT_EQUAL(1, val.asUInt());
JSONTEST_ASSERT_EQUAL(1, val.asLargestUInt());
JSONTEST_ASSERT_EQUAL(true, val.asBool());
JSONTEST_ASSERT_EQUAL("1.50", val.asString());
JSONTEST_ASSERT_EQUAL("1.5", val.asString());

// Small negative number
val = Json::Value(-1.5);
Expand All @@ -1140,7 +1140,7 @@ JSONTEST_FIXTURE( ValueTest, nonIntegers )
JSONTEST_ASSERT_EQUAL(-1, val.asInt());
JSONTEST_ASSERT_EQUAL(-1, val.asLargestInt());
JSONTEST_ASSERT_EQUAL(true, val.asBool());
JSONTEST_ASSERT_EQUAL("-1.50", val.asString());
JSONTEST_ASSERT_EQUAL("-1.5", val.asString());

// A bit over int32 max
val = Json::Value(kint32max + 0.5);
Expand Down Expand Up @@ -1169,7 +1169,7 @@ JSONTEST_FIXTURE( ValueTest, nonIntegers )
JSONTEST_ASSERT_EQUAL(2147483647U, val.asLargestUInt());
#endif
JSONTEST_ASSERT_EQUAL(true, val.asBool());
JSONTEST_ASSERT_EQUAL("2147483647.50", normalizeFloatingPointStr(val.asString()));
JSONTEST_ASSERT_EQUAL("2147483647.5", normalizeFloatingPointStr(val.asString()));

// A bit under int32 min
val = Json::Value(kint32min - 0.5);
Expand All @@ -1196,7 +1196,7 @@ JSONTEST_FIXTURE( ValueTest, nonIntegers )
JSONTEST_ASSERT_EQUAL(-Json::Int64(1)<< 31, val.asLargestInt());
#endif
JSONTEST_ASSERT_EQUAL(true, val.asBool());
JSONTEST_ASSERT_EQUAL("-2147483648.50", normalizeFloatingPointStr(val.asString()));
JSONTEST_ASSERT_EQUAL("-2147483648.5", normalizeFloatingPointStr(val.asString()));

// A bit over uint32 max
val = Json::Value(kuint32max + 0.5);
Expand Down Expand Up @@ -1224,15 +1224,15 @@ JSONTEST_FIXTURE( ValueTest, nonIntegers )
JSONTEST_ASSERT_EQUAL((Json::UInt64(1) << 32)-Json::UInt64(1), val.asLargestUInt());
#endif
JSONTEST_ASSERT_EQUAL(true, val.asBool());
JSONTEST_ASSERT_EQUAL("4294967295.50", normalizeFloatingPointStr(val.asString()));
JSONTEST_ASSERT_EQUAL("4294967295.5", normalizeFloatingPointStr(val.asString()));

val = Json::Value(1.2345678901234);
JSONTEST_ASSERT_STRING_EQUAL( "1.23456789012340", normalizeFloatingPointStr(val.asString()));
JSONTEST_ASSERT_STRING_EQUAL( "1.2345678901234", normalizeFloatingPointStr(val.asString()));

// A 16-digit floating point number.
val = Json::Value(2199023255552000.0f);
JSONTEST_ASSERT_EQUAL(float(2199023255552000), val.asFloat());
JSONTEST_ASSERT_STRING_EQUAL("2199023255552000.", normalizeFloatingPointStr(val.asString()));
JSONTEST_ASSERT_STRING_EQUAL("2199023255552000", normalizeFloatingPointStr(val.asString()));

// A very large floating point number.
val = Json::Value(3.402823466385289e38);
Expand All @@ -1242,7 +1242,7 @@ JSONTEST_FIXTURE( ValueTest, nonIntegers )
// An even larger floating point number.
val = Json::Value(1.2345678e300);
JSONTEST_ASSERT_EQUAL(double(1.2345678e300), val.asDouble());
JSONTEST_ASSERT_STRING_EQUAL("1.234567800000000e+300", normalizeFloatingPointStr(val.asString()));
JSONTEST_ASSERT_STRING_EQUAL("1.2345678e+300", normalizeFloatingPointStr(val.asString()));
}


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