Extract simple integer math into its own module

1 files changed, 75 insertions, 0 deletions

diff --git a/src/lib/intmath/muldiv.c b/src/lib/intmath/muldiv.c
new file mode 100644
index 0000000000..3e627b237a
--- /dev/null
+++ b/src/lib/intmath/muldiv.c
@@ -0,0 +1,75 @@
+/* Copyright (c) 2003-2004, Roger Dingledine
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#include "lib/intmath/muldiv.h"
+#include "lib/err/torerr.h"
+
+#include <stdlib.h>
+
+/** Return the lowest x such that x is at least <b>number</b>, and x modulo
+ * <b>divisor</b> == 0.  If no such x can be expressed as an unsigned, return
+ * UINT_MAX. Asserts if divisor is zero. */
+unsigned
+round_to_next_multiple_of(unsigned number, unsigned divisor)
+{
+  raw_assert(divisor > 0);
+  if (UINT_MAX - divisor + 1 < number)
+    return UINT_MAX;
+  number += divisor - 1;
+  number -= number % divisor;
+  return number;
+}
+
+/** Return the lowest x such that x is at least <b>number</b>, and x modulo
+ * <b>divisor</b> == 0. If no such x can be expressed as a uint32_t, return
+ * UINT32_MAX. Asserts if divisor is zero. */
+uint32_t
+round_uint32_to_next_multiple_of(uint32_t number, uint32_t divisor)
+{
+  raw_assert(divisor > 0);
+  if (UINT32_MAX - divisor + 1 < number)
+    return UINT32_MAX;
+
+  number += divisor - 1;
+  number -= number % divisor;
+  return number;
+}
+
+/** Return the lowest x such that x is at least <b>number</b>, and x modulo
+ * <b>divisor</b> == 0. If no such x can be expressed as a uint64_t, return
+ * UINT64_MAX. Asserts if divisor is zero. */
+uint64_t
+round_uint64_to_next_multiple_of(uint64_t number, uint64_t divisor)
+{
+  raw_assert(divisor > 0);
+  if (UINT64_MAX - divisor + 1 < number)
+    return UINT64_MAX;
+  number += divisor - 1;
+  number -= number % divisor;
+  return number;
+}
+
+/* Helper: return greatest common divisor of a,b */
+static uint64_t
+gcd64(uint64_t a, uint64_t b)
+{
+  while (b) {
+    uint64_t t = b;
+    b = a % b;
+    a = t;
+  }
+  return a;
+}
+
+/* Given a fraction *<b>numer</b> / *<b>denom</b>, simplify it.
+ * Requires that the denominator is greater than 0. */
+void
+simplify_fraction64(uint64_t *numer, uint64_t *denom)
+{
+  raw_assert(denom);
+  uint64_t gcd = gcd64(*numer, *denom);
+  *numer /= gcd;
+  *denom /= gcd;
+}