Fast string to integer

Thu, 29 Aug 2024 00:00:00 +0000

Fast string to integer#

Problem#

In typical cases, strtoul( ) is used to convert strings in decimal or hexadecimal to integers.
However, if strtoul( ) is used repeatedly many times, the processing speed becomes slow.
The following code was repeated 300,000,000 times with strtoul( ), and it took about 5 seconds.

#include <iostream>
#include <chrono>

int main()
{
	const char* hexString = "19AF"; // 0x19AF = 6575

	auto start = std::chrono::high_resolution_clock::now();

	for (int i = 0; i < 300000000; i++)
	{
		int value = strtoul(hexString, NULL, 16);
	}

	auto end = std::chrono::high_resolution_clock::now();
	std::chrono::duration<double, std::milli> elapsed = end - start;
	std::cout << "time: " << elapsed.count() << " ms" << std::endl;

 return 0;
}

Improvement#

Using a LookUp Table (LUT) can process faster than strtoul( ).
The characters included in decimal and hexadecimal strings are as follows.

Performance on Semonan Book

Fast string to integer

Fast string to integer#

Problem#

Improvement#