Faster conversion of integer to string.

zxhio · Dec 30, 2019 · 367a14b · 367a14b
1 parent 81d6209
commit 367a14b
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Showing 5 changed files with 154 additions and 7 deletions.
diff --git a/Log.cpp b/Log.cpp
@@ -10,6 +10,7 @@
 
 #include "Log.h"
 #include "Timestamp.h"
+#include "NumToString.h"
 
 #include <chrono>
 
@@ -333,23 +334,45 @@ LogLine &LogLine::operator<<(char arg) {
     return *this;
 }
 
+LogLine &LogLine::operator<<(int16_t arg) {
+    char tmp[8];
+    int len = util::i16toa(arg, tmp);
+    append(tmp, len);
+    return *this;
+}
+
+LogLine &LogLine::operator<<(uint16_t arg) {
+    char tmp[8];
+    int len = util::u16toa(arg, tmp);
+    append(tmp, len);
+    return *this;
+}
+
 LogLine &LogLine::operator<<(int32_t arg) {
-    append(std::to_string(arg).c_str());
+    char tmp[12];
+    int len = util::i32toa(arg, tmp);
+    append(tmp, len);
     return *this;
 }
 
 LogLine &LogLine::operator<<(uint32_t arg) {
-    append(std::to_string(arg).c_str());
+    char tmp[12];
+    int len = util::u32toa(arg, tmp);
+    append(tmp, len);
     return *this;
 }
 
 LogLine &LogLine::operator<<(int64_t arg) {
-    append(std::to_string(arg).c_str());
+    char tmp[24];
+    int len = util::i64toa(arg, tmp);
+    append(tmp, len);
     return *this;
 }
 
 LogLine &LogLine::operator<<(uint64_t arg) {
-    append(std::to_string(arg).c_str());
+    char tmp[24];
+    int len = util::u64toa(arg, tmp);
+    append(tmp, len);
     return *this;
 }
 
@@ -376,7 +399,7 @@ void setRollSize(uint32_t nMb) { LimLog::singleton()->setRollSize(nMb); }
 LogLevel getLogLevel() { return LimLog::singleton()->getLogLevel(); }
 
 // Stringify log level with width of 5.
-std::string stringifyLogLevel(LogLevel level) {
+const char *stringifyLogLevel(LogLevel level) {
     switch (level) {
     case LogLevel::FATAL:
         return "FATAL";

diff --git a/Log.h b/Log.h
@@ -162,6 +162,8 @@ class LogLine {
     /// Overloaded functions with various types of argument.
     LogLine &operator<<(bool arg);
     LogLine &operator<<(char arg);
+    LogLine &operator<<(int16_t arg);
+    LogLine &operator<<(uint16_t arg);
     LogLine &operator<<(int32_t arg);
     LogLine &operator<<(uint32_t arg);
     LogLine &operator<<(int64_t arg);
@@ -185,7 +187,7 @@ void setLogLevel(LogLevel level);
 
 /// Get log level.
 LogLevel getLogLevel();
-std::string stringifyLogLevel(LogLevel level);
+const char *stringifyLogLevel(LogLevel level);
 
 /// Set log file (basename and dir, no suffix), defalut `./run`.
 /// The Program will automatically add suffix (`.log`).

diff --git a/Makefile b/Makefile
@@ -3,7 +3,7 @@ CXX = g++
 CFLAGS = -std=c++11 -Wall -O3 -g -fno-common
 LIBS = -L. -lpthread
 
-LIB_SRCS = Timestamp.cpp Log.cpp
+LIB_SRCS = Timestamp.cpp Log.cpp NumToString.cpp
 LIB_OBJS = $(LIB_SRCS:.cpp=.o)
 
 TEST_SRCS = LogTest.cpp

diff --git a/NumToString.cpp b/NumToString.cpp
@@ -0,0 +1,96 @@
+//===- NumToString.cpp - Number to string -----------------------*- C++ -*-===//
+//
+/// \file
+/// Faster conversion for number to string with look up digits table.
+//
+// Author:  zxh(definezxh@163.com)
+// Date:    2019/12/29 17:48:39
+//===----------------------------------------------------------------------===//
+
+#include "NumToString.h"
+
+#include <type_traits>
+
+namespace util {
+
+// The digits table is used to look up for number within 100.
+// Each two character corresponds to one digit and ten digits.
+static const char DigitsTable[200] = {
+    '0', '0', '0', '1', '0', '2', '0', '3', '0', '4', '0', '5', '0', '6', '0',
+    '7', '0', '8', '0', '9', '1', '0', '1', '1', '1', '2', '1', '3', '1', '4',
+    '1', '5', '1', '6', '1', '7', '1', '8', '1', '9', '2', '0', '2', '1', '2',
+    '2', '2', '3', '2', '4', '2', '5', '2', '6', '2', '7', '2', '8', '2', '9',
+    '3', '0', '3', '1', '3', '2', '3', '3', '3', '4', '3', '5', '3', '6', '3',
+    '7', '3', '8', '3', '9', '4', '0', '4', '1', '4', '2', '4', '3', '4', '4',
+    '4', '5', '4', '6', '4', '7', '4', '8', '4', '9', '5', '0', '5', '1', '5',
+    '2', '5', '3', '5', '4', '5', '5', '5', '6', '5', '7', '5', '8', '5', '9',
+    '6', '0', '6', '1', '6', '2', '6', '3', '6', '4', '6', '5', '6', '6', '6',
+    '7', '6', '8', '6', '9', '7', '0', '7', '1', '7', '2', '7', '3', '7', '4',
+    '7', '5', '7', '6', '7', '7', '7', '8', '7', '9', '8', '0', '8', '1', '8',
+    '2', '8', '3', '8', '4', '8', '5', '8', '6', '8', '7', '8', '8', '8', '9',
+    '9', '0', '9', '1', '9', '2', '9', '3', '9', '4', '9', '5', '9', '6', '9',
+    '7', '9', '8', '9', '9'};
+
+static int lut_utoa(uint64_t number, char *to) {
+    char buf[24];
+    char *p = buf;
+    int length = 0;
+
+    while (number >= 100) {
+        const unsigned idx = (number % 100) << 1;
+        number /= 100;
+        *p++ = DigitsTable[idx + 1];
+        *p++ = DigitsTable[idx];
+    }
+
+    if (number < 10) {
+        *p++ = number + '0';
+    } else {
+        const unsigned idx = number << 1;
+        *p++ = DigitsTable[idx + 1];
+        *p++ = DigitsTable[idx];
+    }
+
+    length = p - buf;
+
+    do {
+        *to++ = *--p;
+    } while (p != buf);
+    *to = '\0';
+
+    return length;
+}
+
+int lut_itoa(int64_t number, char *to) {
+    uint64_t n = static_cast<uint64_t>(number);
+    int sign = 0;
+    if (number < 0) {
+        *to++ = '-';
+        n = ~n + 1;
+        sign = 1;
+    }
+
+    return lut_utoa(n, to) + sign;
+}
+
+int u16toa(uint16_t number, char *to) {
+    return lut_utoa(static_cast<uint16_t>(number), to);
+}
+int u32toa(uint32_t number, char *to) {
+    return lut_utoa(static_cast<uint32_t>(number), to);
+}
+int u64toa(uint64_t number, char *to) {
+    return lut_utoa(static_cast<uint64_t>(number), to);
+}
+
+int i16toa(int16_t number, char *to) {
+    return lut_itoa(static_cast<int16_t>(number), to);
+}
+int i32toa(int32_t number, char *to) {
+    return lut_itoa(static_cast<int32_t>(number), to);
+}
+int i64toa(int64_t number, char *to) {
+    return lut_itoa(static_cast<int64_t>(number), to);
+}
+
+} // namespace util
diff --git a/NumToString.h b/NumToString.h
@@ -0,0 +1,26 @@
+//===- NumToString.h - Number to string -------------------------*- C++ -*-===//
+//
+/// \file
+/// Faster conversion for number to string.
+//
+// Author:  zxh(definezxh@163.com)
+// Date:    2019/12/29 17:45:31
+//===----------------------------------------------------------------------===//
+
+#pragma once
+
+#include <stdint.h>
+
+namespace util {
+
+/// Conversion unsigned integer to string \p to , and return string length.
+int u16toa(uint16_t number, char *to);
+int u32toa(uint32_t number, char *to);
+int u64toa(uint64_t number, char *to);
+
+/// Conversion signed integer to string \p to , and return string length.
+int i16toa(int16_t number, char *to);
+int i32toa(int32_t number, char *to);
+int i64toa(int64_t number, char *to);
+
+} // namespace util