#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

struct thread_arg {
  const float *A;
  const float *B;
  float *C;
  int M;
  int N;
  int K;
  int num_threads;
  int rank; /* id of this thread */
} args[256];
static pthread_t threads[256];

static void *matmul_kernel(void *arg) {
  /*
  TODO: FILL IN HERE
  */

  struct thread_arg *input = (struct thread_arg *)arg;

  const float *A = (*input).A;
  const float *B = (*input).B;
  float *C = (*input).C;
  int M = (*input).M;
  int N = (*input).N;
  int K = (*input).K;
  int num_threads = (*input).num_threads;
  int rank = (*input).rank;

  int div = M / num_threads;
  /*
  C[i][j] = sum of A[i][k]* B[k][j]
  C[i][j] = C[i*N + j]
  A[i][k] = A[i*K + j]
  B[k][j] = B[k*N + j]
  */
  for (int k = 0; k < N; ++k) {
    for (int i = rank * div; i < (rank + 1) * div; ++i) {
      for (int j = 0; j < K; ++j) {
        C[i * N + j] += A[i * K + k] * B[k * N + j];
      }
    }
  }

  if (M % num_threads != 0) {
    for (int k = 0; k < N; ++k) {
      for (int i = div * num_threads; i < M; ++i) {
        for (int j = 0; j < K; ++j) {
          C[i * N + j] += A[i * K + k] * B[k * N + j];
        }
      }
    }
  }
  return NULL;
}

void matmul(const float *A, const float *B, float *C, int M, int N, int K,
            int num_threads) {

  if (num_threads > 256) {
    fprintf(stderr, "num_threads must be <= 256\n");
    exit(EXIT_FAILURE);
  }

  int err;
  for (int t = 0; t < num_threads; ++t) {
    args[t].A = A, args[t].B = B, args[t].C = C, args[t].M = M, args[t].N = N,
    args[t].K = K, args[t].num_threads = num_threads, args[t].rank = t;
    err = pthread_create(&threads[t], NULL, matmul_kernel, (void *)&args[t]);
    if (err) {
      printf("pthread_create(%d) failed with err %d\n", t, err);
      exit(EXIT_FAILURE);
    }
  }

  for (int t = 0; t < num_threads; ++t) {
    err = pthread_join(threads[t], NULL);
    if (err) {
      printf("pthread_join(%d) failed with err %d\n", t, err);
      exit(EXIT_FAILURE);
    }
  }
}