align.c

代码优化,有效使用内存,透视优化技术,对比优化方法,如果你在追求代码效率的最大化,该资源你不能不读.

/* ---------------------------------------------------------------------------
 *
 *						UTILITY DEMONSTRATING THE INFLUENCE
 *		OF ADDRESS ALIGNMENT ON THE PROCESSING SPEED OF LARGE DATA BLOCKS
 *		=================================================================
 *
 * Build 0x001 06.07.2002
--------------------------------------------------------------------------- */
// CONFIGURATION
#define BLOCK_SIZE		(8*M)			// size of the processed block

#include <DoCPU.h>
main()
{
	int *p1;
	int a, x = 0;

	// TITLE
	PRINT("= = = influence of address alignment on the processing speed of large data blocks = = =\n");
	PRINT_TITLE;

	// allocating memory
	p1 = malloc(BLOCK_SIZE);


	/*------------------------------------------------------------------------
	 *
	 *						WITHOUT UNROLLING THE LOOP
	 *
	----------------------------------------------------------------------- */
	VVV;
	A_BEGIN(0)
		// aligned read
		for (a = 0; a < BLOCK_SIZE; a += sizeof(int))
			x+= *(int *) ((char *)p1 + a);
	A_END(0)

	VVV;
	A_BEGIN(1)
		// unaligned read
		for (a = 0; a < BLOCK_SIZE; a += sizeof(int))
			x+= *(int *) ((char *)p1 + a + 1 /* <- unalign */);
		A_END(1)

	VVV;
	A_BEGIN(2)
		// aligned write
		for (a = 0; a < BLOCK_SIZE; a += sizeof(int))
			*(int *) ((char *)p1 + a) = x;
	A_END(2)

	VVV;
	A_BEGIN(3)
		// unaligned write
		for (a = 0; a < BLOCK_SIZE; a += sizeof(int))
			*(int *) ((char *)p1 + a + 1) = x;
	A_END(3)

	/*------------------------------------------------------------------------
	 *
	 *					WITH LOOP UNROLLING BY 8 ITERATIONS
	 *
	----------------------------------------------------------------------- */
	VVV;
	A_BEGIN(4)
		// aligned read
		for (a = 0; a < BLOCK_SIZE; a += 8 * sizeof(int))
		{
			x += *(int *) ((char *)p1 + a + 0 * sizeof(int));
			x += *(int *) ((char *)p1 + a + 1 * sizeof(int));
			x += *(int *) ((char *)p1 + a + 2 * sizeof(int));
			x += *(int *) ((char *)p1 + a + 3 * sizeof(int));
			x += *(int *) ((char *)p1 + a + 4 * sizeof(int));
			x += *(int *) ((char *)p1 + a + 5 * sizeof(int));
			x += *(int *) ((char *)p1 + a + 6 * sizeof(int));
			x += *(int *) ((char *)p1 + a + 7 * sizeof(int));
		}
	A_END(4)


	VVV;
	A_BEGIN(5)
		// unaligned read
		for (a = 0; a < BLOCK_SIZE; a += 8 * sizeof(int))
		{
			x += *(int *) ((char *)p1 + a + 0 * sizeof(int) + 1);
			x += *(int *) ((char *)p1 + a + 1 * sizeof(int) + 1);
			x += *(int *) ((char *)p1 + a + 2 * sizeof(int) + 1);
			x += *(int *) ((char *)p1 + a + 3 * sizeof(int) + 1);
			x += *(int *) ((char *)p1 + a + 4 * sizeof(int) + 1);
			x += *(int *) ((char *)p1 + a + 5 * sizeof(int) + 1);
			x += *(int *) ((char *)p1 + a + 6 * sizeof(int) + 1);
			x += *(int *) ((char *)p1 + a + 7 * sizeof(int) + 1);
		}
	A_END(5)


	VVV;
	A_BEGIN(6)
		// aligned write
		for (a = 0; a < BLOCK_SIZE; a += 8 * sizeof(int))
		{
			*(int *) ((char *)p1 + a + 0 * sizeof(int)) = x;
			*(int *) ((char *)p1 + a + 1 * sizeof(int)) = x;
			*(int *) ((char *)p1 + a + 2 * sizeof(int)) = x;
			*(int *) ((char *)p1 + a + 3 * sizeof(int)) = x;
			*(int *) ((char *)p1 + a + 4 * sizeof(int)) = x;
			*(int *) ((char *)p1 + a + 5 * sizeof(int)) = x;
			*(int *) ((char *)p1 + a + 6 * sizeof(int)) = x;
			*(int *) ((char *)p1 + a + 7 * sizeof(int)) = x;
		}
	A_END(6)


	VVV;
	A_BEGIN(7)
		// unaligned write
		for (a = 0; a < BLOCK_SIZE; a += 8 * sizeof(int))
		{
			*(int *) ((char *)p1 + a + 0 * sizeof(int) + 1) = x;
			*(int *) ((char *)p1 + a + 1 * sizeof(int) + 1) = x;
			*(int *) ((char *)p1 + a + 2 * sizeof(int) + 1) = x;
			*(int *) ((char *)p1 + a + 3 * sizeof(int) + 1) = x;
			*(int *) ((char *)p1 + a + 4 * sizeof(int) + 1) = x;
			*(int *) ((char *)p1 + a + 5 * sizeof(int) + 1) = x;
			*(int *) ((char *)p1 + a + 6 * sizeof(int) + 1) = x;
			*(int *) ((char *)p1 + a + 7 * sizeof(int) + 1) = x;
		}
	A_END(7)
	
	// console output
	Lx_OUT("unalign read  without unroll",Ax_GET(0),Ax_GET(1));
	Lx_OUT("unalign write without unroll",Ax_GET(2),Ax_GET(3));
	Lx_OUT("unalign read  with    unroll",Ax_GET(4),Ax_GET(5));
	Lx_OUT("unalign write with    unroll",Ax_GET(6),Ax_GET(7));
}