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loop-optimizations/loop-optimization.c

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+/*
+ * loop-optimization.c
+ *
+ * Naomi Dickerson 2014
+ * Coursework for Wu-chang Feng's NB class
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define SIZE 1000
+
+typedef int data_t;
+
+void inner4(data_t* u, data_t* v, data_t* dest, int vec_length) {
+ // loop with local variables
+ long int i;
+ int length = vec_length;
+ data_t *udata = u;
+ data_t *vdata = v;
+ data_t sum = (data_t) 0;
+
+ for (i = 0; i < length; i++) {
+ sum = sum + udata[i] * vdata[i];
+ }
+
+ *dest = sum;
+}
+
+void inner5(data_t* u, data_t* v, data_t* dest, int vec_length) {
+ // loop with 4-way data unrolling
+ long int i;
+ int length = vec_length;
+ data_t *udata = u;
+ data_t *vdata = v;
+ data_t sum = (data_t) 0;
+
+ for (i = 0; i < (length - 3); i += 4) {
+ sum += udata[i] * vdata[i];
+ sum += udata[i+1] * vdata[i+1];
+ sum += udata[i+2] * vdata [i+2];
+ sum += udata[i+3] * vdata [i+3];
+ }
+
+ for (; i < length; i++) {
+ sum += udata[i] * vdata[i];
+ }
+
+ *dest = sum;
+}
+
+void inner6(data_t* u, data_t* v, data_t* dest, int vec_length) {
+ // loop with four parallel accumulators
+ long int i;
+ int length = vec_length;
+ data_t *udata = u;
+ data_t *vdata = v;
+ data_t sum1 = (data_t) 0;
+ data_t sum2 = (data_t) 0;
+ data_t sum3 = (data_t) 0;
+ data_t sum4 = (data_t) 0;
+
+ for (i = 0; i < (length - 3); i += 4) {
+ sum1 += udata[i] * vdata[i];
+ sum2 += udata[i+1] * vdata[i+1];
+ sum3 += udata[i+2] * vdata [i+2];
+ sum4 += udata[i+3] * vdata [i+3];
+ }
+
+ for (; i < length; i++) {
+ sum1 += udata[i] * vdata[i];
+ }
+
+ *dest = sum1 + sum2 + sum3 + sum4;
+}
+
+void inner7(data_t* u, data_t* v, data_t* dest, int vec_length) {
+ // loop with unrolling and reassociation
+ long int i;
+ int length = vec_length;
+ data_t *udata = u;
+ data_t *vdata = v;
+ data_t sum = (data_t) 0;
+
+ for (i = 0; i < (length - 3); i += 4) {
+ sum = sum + ((udata[i] * vdata[i]) + (udata[i+1] * vdata[i+1]));
+ sum = sum + ((udata[i+2] * vdata [i+2]) + (udata[i+3] * vdata [i+3]));
+ }
+
+ for (; i < length; i++) {
+ sum += udata[i] * vdata[i];
+ }
+
+ *dest = sum;
+}
+
+int main() {
+ int vec_length = SIZE;
+ data_t vec_u[SIZE];
+ data_t vec_v[SIZE];
+ data_t *dest;
+
+ // Fill vectors arbitrarily for testing.
+ for (int i = 0; i < SIZE; i++) {
+ vec_u[i] = (data_t) i;
+ vec_v[i] = (data_t) i + 1;
+ }
+
+ inner4(vec_u, vec_v, dest, vec_length);
+ inner5(vec_u, vec_v, dest, vec_length);
+ inner6(vec_u, vec_v, dest, vec_length);
+ inner7(vec_u, vec_v, dest, vec_length);
+
+ return 0;
+}