gint_strcat/src/string.c

#include <string.h>
#include <stdint.h>

//---
//	Memory manipulation.
//---

/*
	memcpy()
	Copies a memory area. A smart copy is performed if possible.

	@arg	destination
	@arg	source
	@arg	byte_number
*/
void *memcpy(void *d, const void *s, size_t n)
{
	uint8_t		*dest = (uint8_t *)d;
	const uint8_t	*src  = (const uint8_t *)s;

	// A long-based copy needs the source and destination to be 4-aligned
	// at the same time.
	if(((intptr_t)dest & 3) == ((intptr_t)src & 3))
	{
		// Getting to a long offset.
		while((intptr_t)dest & 3)
		{
			*dest++ = *src++;
			n--;
		}

		// Copying groups of four bytes.
		while(n >= 4)
		{
			*((uint32_t *)dest) = *((const uint32_t *)src);

			dest += 4, src += 4;
			n -= 4;
		}

		// Ending the copy.
		while(n)
		{
			*dest++ = *src++;
			n--;
		}
	}

	// Or we could try a word-based copy.
	else if(((intptr_t)dest & 1) == ((intptr_t)src & 1))
	{
		// Getting to a word offset.
		if((intptr_t)dest & 1)
		{
			*dest++ = *src++;
			n--;
		}

		// Copying groups of two bytes.
		while(n >= 2)
		{
			*((uint16_t *)dest) = *((const uint16_t *)src);

			dest += 2, src += 2;
			n -= 2;
		}

		// Ending the copy.
		while(n)
		{
			*dest++ = *src++;
			n--;
		}
	}

	// In some cases we can just perform a raw copy.
	else while(n)
	{
		*dest++ = *src++;
		n--;
	}

	return d;
}

/*
	memset()
	Sets the contents of a memory area. A smart copy is performed.

	@arg	area
	@arg	byte		Byte to write in the area.
	@arg	byte_number
*/
void *memset(void *d, int byte, size_t byte_number)
{
	uint8_t *dest = (uint8_t *)d;
	unsigned short word = (byte << 8) | byte;
	unsigned int longword = (word << 16) | word;

	// When the area is small, simply copying using byte operations. The
	// minimum length used for long operations must be at least 3.
	if(byte_number < 8)
	{
		while(byte_number)
		{
			*dest++ = byte;
			byte_number--;
		}

		return d;
	}

	// Reaching a long offset.
	while((intptr_t)dest & 3)
	{
		*dest++ = byte;
		byte_number--;
	}
	// Copying using long operations.
	while(byte_number >= 4)
	{
		*((uint32_t *)dest) = longword;
		dest += 4;
		byte_number -= 4;
	}
	// Ending the copy.
	while(byte_number)
	{
		*dest++ = byte;
		byte_number--;
	}

	return d;
}