README.md

Performance

Before this lab, we need read some articles:

• README
• Writeup

PAY ATTENTION: because we just self-study, so we just need to optimize the kernels.c, rather than care scores mentioned by README.

Structure

Initially, we look at the useful files::

• README: An introduce file, although it help nothing.
• kernels.c: This is the file you will be modifying and handing in.

Then, we should execute make clean and make to build this lab.

Introduction

Two process of image:

• rotate: totates an image counter-clockwise 90˚.
  • transpose: for each (i, j) pair, swap M[i][j] and M[j][i].
  • exchange rows: row i is exchanged with row N-1-i.
• smooth: replace every pixel value with teh average of all the pixels around it, and the special case is bound grids.

Implementation Overview

Data Structures:

typedef struct {
   unsigned short red;
   unsigned short green;
   unsigned short blue;
} pixel;

An image I is represented as a one-dimensional array of pixels, where the (i,j)th pixel is I[RIDX(i,j,n)].

where:

#define RIDX(i,j,n) ((i)*(n)+(j))

solution

From dst[RIDX(dim-1-j, i, dim)] = src[RIDX(i, j, dim)];

we know that: dst[dim * dim - dim - j * dim + i] = src[i * dim + j];

Rotate

loop unrolling.

Smooth

compute the grid one by one.

Think

I think optimization too much is harmful...