example.c

   1 #!/usr/bin/env cscript
   2
   3 /* SPDX-License-Identifier: GPL-2.0
   4  *
   5  * Copyright (C) 2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
   6  */
   7
   8 #define _GNU_SOURCE
   9
  10 #include <stdint.h>
  11 #include <stddef.h>
  12 #include <stdlib.h>
  13 #include <stdio.h>
  14 #include <inttypes.h>
  15 #include <errno.h>
  16
  17 enum { PASCALS_TRIANGLE_MAX_ROWS_FOR_UINT64 = 68 };
  18
  19 static inline size_t cord(size_t a, size_t b)
  20 {
  21         return a * (a + 1) / 2 + b;
  22 }
  23
  24 static uint64_t *create_pascals_triangle(size_t num_rows)
  25 {
  26         uint64_t *triangle;
  27         size_t i, j;
  28
  29         if (!num_rows || num_rows > PASCALS_TRIANGLE_MAX_ROWS_FOR_UINT64) {
  30                 errno = EINVAL;
  31                 return NULL;
  32         }
  33
  34         triangle = reallocarray(NULL, cord(num_rows, 0), sizeof(*triangle));
  35         if (!triangle)
  36                 return NULL;
  37
  38         for (i = 0; i < num_rows; ++i) {
  39                 triangle[cord(i, 0)] = triangle[cord(i, i)] = 1;
  40                 for (j = 1; j < i; ++j)
  41                         triangle[cord(i, j)] = triangle[cord(i - 1, j - 1)] + triangle[cord(i - 1, j)];
  42         }
  43
  44         return triangle;
  45 }
  46
  47 static void print_pascals_triangle(FILE *file, const uint64_t *triangle, size_t num_rows)
  48 {
  49         size_t i, j;
  50
  51         for (i = 0; i < num_rows; ++i) {
  52                 for (j = 0; j < i + 1; ++j)
  53                         fprintf(file, "%" PRIu64 " ", triangle[cord(i, j)]);
  54                 fputc('\n', file);
  55         }
  56 }
  57
  58 int main(int argc, char *argv[])
  59 {
  60         uint64_t *triangle;
  61         size_t num_rows;
  62         char *endptr;
  63
  64         if (argc != 2) {
  65                 fprintf(stderr, "Usage: %s ROWS\n", argv[0]);
  66                 return 1;
  67         }
  68
  69         num_rows = strtoul(argv[1], &endptr, 10);
  70         if (!*argv[1] || *endptr) {
  71                 fprintf(stderr, "ERROR: `%s' is not a valid number\n", argv[1]);
  72                 return 1;
  73         }
  74
  75         triangle = create_pascals_triangle(num_rows);
  76         if (!triangle) {
  77                 perror("ERROR: unable to create triangle");
  78                 return 1;
  79         }
  80         print_pascals_triangle(stdout, triangle, num_rows);
  81         free(triangle);
  82
  83         return 0;
  84 }