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JSON: Slightly improve json::encode() performance

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More efficient string concatenation combined with a lookup table for
JSON encodings leads to 2% improvement for "export" performance test,
3% improvement for "import" performance test.
This commit is contained in:
Wilhelm Schuermann 2015-11-22 16:09:08 +01:00
parent d6d867c1cf
commit e5916d0feb
1 changed files with 51 additions and 11 deletions
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62
src/JSON.cpp
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@ -30,6 +30,41 @@
#include <i18n.h>
#include <utf8.h>
const char *json_encode[] = {
"\x00", "\x01", "\x02", "\x03", "\x04", "\x05", "\x06", "\x07",
"\\b", "\\t", "\\n", "\x0b", "\\f", "\\r", "\x0e", "\x0f",
"\x10", "\x11", "\x12", "\x13", "\x14", "\x15", "\x16", "\x17",
"\x18", "\x19", "\x1a", "\x1b", "\x1c", "\x1d", "\x1e", "\x1f",
"\x20", "\x21", "\\\"", "\x23", "\x24", "\x25", "\x26", "\x27",
"\x28", "\x29", "\x2a", "\x2b", "\x2c", "\x2d", "\x2e", "\\/",
"\x30", "\x31", "\x32", "\x33", "\x34", "\x35", "\x36", "\x37",
"\x38", "\x39", "\x3a", "\x3b", "\x3c", "\x3d", "\x3e", "\x3f",
"\x40", "\x41", "\x42", "\x43", "\x44", "\x45", "\x46", "\x47",
"\x48", "\x49", "\x4a", "\x4b", "\x4c", "\x4d", "\x4e", "\x4f",
"\x50", "\x51", "\x52", "\x53", "\x54", "\x55", "\x56", "\x57",
"\x58", "\x59", "\x5a", "\x5b", "\\\\", "\x5d", "\x5e", "\x5f",
"\x60", "\x61", "\x62", "\x63", "\x64", "\x65", "\x66", "\x67",
"\x68", "\x69", "\x6a", "\x6b", "\x6c", "\x6d", "\x6e", "\x6f",
"\x70", "\x71", "\x72", "\x73", "\x74", "\x75", "\x76", "\x77",
"\x78", "\x79", "\x7a", "\x7b", "\x7c", "\x7d", "\x7e", "\x7f",
"\x80", "\x81", "\x82", "\x83", "\x84", "\x85", "\x86", "\x87",
"\x88", "\x89", "\x8a", "\x8b", "\x8c", "\x8d", "\x8e", "\x8f",
"\x90", "\x91", "\x92", "\x93", "\x94", "\x95", "\x96", "\x97",
"\x98", "\x99", "\x9a", "\x9b", "\x9c", "\x9d", "\x9e", "\x9f",
"\xa0", "\xa1", "\xa2", "\xa3", "\xa4", "\xa5", "\xa6", "\xa7",
"\xa8", "\xa9", "\xaa", "\xab", "\xac", "\xad", "\xae", "\xaf",
"\xb0", "\xb1", "\xb2", "\xb3", "\xb4", "\xb5", "\xb6", "\xb7",
"\xb8", "\xb9", "\xba", "\xbb", "\xbc", "\xbd", "\xbe", "\xbf",
"\xc0", "\xc1", "\xc2", "\xc3", "\xc4", "\xc5", "\xc6", "\xc7",
"\xc8", "\xc9", "\xca", "\xcb", "\xcc", "\xcd", "\xce", "\xcf",
"\xd0", "\xd1", "\xd2", "\xd3", "\xd4", "\xd5", "\xd6", "\xd7",
"\xd8", "\xd9", "\xda", "\xdb", "\xdc", "\xdd", "\xde", "\xdf",
"\xe0", "\xe1", "\xe2", "\xe3", "\xe4", "\xe5", "\xe6", "\xe7",
"\xe8", "\xe9", "\xea", "\xeb", "\xec", "\xed", "\xee", "\xef",
"\xf0", "\xf1", "\xf2", "\xf3", "\xf4", "\xf5", "\xf6", "\xf7",
"\xf8", "\xf9", "\xfa", "\xfb", "\xfc", "\xfd", "\xfe", "\xff"
};
////////////////////////////////////////////////////////////////////////////////
json::value* json::value::parse (Nibbler& nibbler)
{
@ -379,25 +414,30 @@ std::string json::encode (const std::string& input)
std::string output;
output.reserve ((input.size () * 6) / 5); // 20% increase.
for (auto& i : input)
auto last = input.begin ();
for (auto i = input.begin (); i != input.end (); ++i)
{
switch (i)
switch (*i)
{
// Simple translations.
case '"': output += "\\\""; break;
case '\\': output += "\\\\"; break;
case '/': output += "\\/"; break;
case '\b': output += "\\b"; break;
case '\f': output += "\\f"; break;
case '\n': output += "\\n"; break;
case '\r': output += "\\r"; break;
case '\t': output += "\\t"; break;
case '"':
case '\\':
case '/':
case '\b':
case '\f':
case '\n':
case '\r':
case '\t':
output.append (last, i);
output += json_encode[(unsigned char)(*i)];
last = i + 1;
// Default NOP.
default: output += i; break;
}
}
output.append (last, input.end ());
return output;
}