#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
struct matrix_s {
char matrixName[50];
size_t columns;
size_t rows;
float* data;
};
typedef struct matrix_s matrix_t;
void m_init(matrix_t *t, size_t columns, size_t rows) {
t->rows = rows;
t->columns = columns;
t->data = calloc(rows * columns, sizeof(*t->data));
if (t->data == NULL) abort();
}
size_t m_columns(const matrix_t *t) {
return t->columns;
}
size_t m_rows(const matrix_t *t) {
return t->rows;
}
// matrix_get
// (x,y) = (col,row) always in that order
float *m_get(const matrix_t *t, size_t x, size_t y) {
assert(x < m_columns(t));
assert(y < m_rows(t));
// __UNCONST
// see for example `char *strstr(const char *haystack, ...`
// it takes `const char*` but returns `char*` nonetheless.
return (float*)&t->data[t->rows * x + y];
}
// fill matrix with a fancy patterns just so it's semi-unique
void m_init_seq(matrix_t *t, size_t columns, size_t rows) {
m_init(t, columns, rows);
for (size_t i = 0; i < t->columns; ++i) {
for (size_t j = 0; j < t->rows; ++j) {
*m_get(t, i, j) = i + 100 * j;
}
}
}
void m_print(const matrix_t *t) {
printf("matrix %p\n", (void*)t->data);
for (size_t i = 0; i < t->columns; ++i) {
for (size_t j = 0; j < t->rows; ++j) {
printf("%5g\t", *m_get(t, i, j));
}
printf("\n");
}
printf("\n");
}
void m_multiply(matrix_t *out, const matrix_t *a, const matrix_t *b) {
assert(m_columns(b) == m_rows(a));
assert(m_columns(out) == m_columns(a));
assert(m_rows(out) == m_rows(b));
// Index from 0, not from 1
// don't do `(col-1) + (row-1)` strange things
for (size_t col = 0; col < m_columns(out); ++col) {
for (size_t row = 0; row < m_rows(out); ++row) {
float sum = 0;
for (size_t i = 0; i < m_rows(a); ++i) {
sum += *m_get(a, col, i) * *m_get(b, i, row);
}
*m_get(out, col, row) = sum;
}
}
}
int main()
{
matrix_t our_matrix[100];
m_init_seq(&our_matrix[0], 4, 2);
m_init_seq(&our_matrix[1], 2, 3);
m_print(&our_matrix[0]);
m_print(&our_matrix[1]);
m_init(&our_matrix[2], 4, 3);
m_multiply(&our_matrix[2], &our_matrix[0], &our_matrix[1]);
m_print(&our_matrix[2]);
return 0;
}
