From 0e8d73bb3edcc8bdff6e3ded442b66f68265059a Mon Sep 17 00:00:00 2001
From: Sebastiano Tronto <sebastiano.tronto@gmail.com>
Date: Sun, 21 Jun 2020 23:01:57 +0200
Subject: First push

---
 src/utils.h | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 src/utils.h

(limited to 'src/utils.h')

diff --git a/src/utils.h b/src/utils.h
new file mode 100644
index 0000000..b24ccb2
--- /dev/null
+++ b/src/utils.h
@@ -0,0 +1,54 @@
+#define min(a,b) (((a) < (b)) ? (a) : (b))
+#define max(a,b) (((a) > (b)) ? (a) : (b))
+#define abs(a)   (((a) > 0)   ? (a) : (-(a)))
+
+/* Some useful constants */
+#define pow2to11    2048
+#define pow2to12    4096
+#define pow3to7     2187
+#define pow3to8     6561
+#define pow12to4    20736
+#define factorial4  24
+#define factorial6  720
+#define factorial8  40320
+#define factorial12 479001600
+#define binom12on4  495
+#define binom8on4   70
+
+void swap(int *a, int *b);
+
+/* Hardcoded factorial of small numbers (n<=12). */
+extern int factorial[13];
+
+/* Converts the integer a to its representation in base b (first n digits
+ * only) and saves the result in r. */
+void int_to_digit_array(int a, int b, int n, int *r);
+ 
+/* Converts the array of n digits a to a integer using base b. */
+int digit_array_to_int(int *a, int n, int b);
+ 
+/* Converts a permutation on [0..(n-1)] into the integer i which is the index
+ * of the permutation in the sorted list of all n! such permutations.
+ * Only works for n<=12. */
+int perm_to_index(int *a, int n);
+
+/* Converts a permutation index to the actual permutation as an array
+ * (see perm_to_index) and saves the result to r. */
+void index_to_perm(int p, int n, int *r);
+
+/* Converts a k-element subset of a set with an element from an array of n
+ * elements, of which k are 1 and n-k are 0, to its index in the sorted list
+ * of all such subsets.
+ * Works only for n <= 12. */
+int subset_to_index(int *a, int n, int k);
+ 
+/* Inverse of the above */
+void index_to_subset(int s, int n, int k, int *r);
+
+/* Converts the first n-1 digits of a number to an array a of digits in base b;
+ * then adds one element to the array, so that the sum of the elements of a is
+ * zero modulo b.
+ * This is used for determing the edge orientation from an 11-bits integer or
+ * the corner orientation from a 7-trits integer. */
+void int_to_sum_zero_array(int x, int b, int n, int *a);
+
-- 
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