From 234eb62226d665880b23e808ba2817fed66a7c76 Mon Sep 17 00:00:00 2001
From: Enno Rehling <enno.rehling@gmail.com>
Date: Fri, 24 Feb 2017 17:51:35 +0100
Subject: [PATCH] short and sweet math with fractions. goinf to use this for
 magres.

---
 src/test_eressea.c      |  2 ++
 src/util/CMakeLists.txt |  1 +
 src/util/variant.c      | 54 +++++++++++++++++++++++++++++------------
 src/util/variant.h      |  1 +
 src/util/variant.test.c | 28 +++++++++++++++++++++
 5 files changed, 71 insertions(+), 15 deletions(-)
 create mode 100644 src/util/variant.test.c

diff --git a/src/test_eressea.c b/src/test_eressea.c
index 4ffe1f19c..1d991725f 100644
--- a/src/test_eressea.c
+++ b/src/test_eressea.c
@@ -6,6 +6,7 @@
 #include <string.h>
 #include <stdlib.h>
 #include <util/log.h>
+#include <util/variant.h>
 
 #pragma warning(disable: 4210)
 
@@ -85,6 +86,7 @@ int RunAllTests(int argc, char *argv[])
     ADD_SUITE(unicode);
     ADD_SUITE(strings);
     ADD_SUITE(log);
+    ADD_SUITE(variant);
     ADD_SUITE(rng);
     /* items */
     ADD_SUITE(xerewards);
diff --git a/src/util/CMakeLists.txt b/src/util/CMakeLists.txt
index 743ff4d88..91ed118ae 100644
--- a/src/util/CMakeLists.txt
+++ b/src/util/CMakeLists.txt
@@ -28,6 +28,7 @@ log.test.c
 # translation.test.c
 umlaut.test.c
 unicode.test.c
+variant.test.c
 # xml.test.c
 )
 
diff --git a/src/util/variant.c b/src/util/variant.c
index e3461f861..74d7adb1c 100644
--- a/src/util/variant.c
+++ b/src/util/variant.c
@@ -1,16 +1,39 @@
+#include <platform.h>
 #include "variant.h"
+
+#include <assert.h>
 #include <limits.h>
 
-static int lcd(int a, int b) {
-    return a * b;
+static int gcd(int a, int b) {
+    const int primes[] = { 3, 5, 7, 11, 13, 17, 19, 23, 0 };
+    int i = 0, g = 1, p = 2;
+    while (p && p <= a && p <= b) {
+        if (a % p == 0 && b % p == 0) {
+            a /= p;
+            b /= p;
+            g *= p;
+        }
+        else {
+            p = primes[i++];
+        }
+    }
+    return g;
 }
 
-variant frac_add(variant a, variant b)
+static int lcm(int a, int b) {
+    int x;
+    if (a == b) return a;
+    x = (a * b);
+    x = (x > 0 ? x : -x) / gcd(a, b);
+    return x;
+}
+
+variant frac_make(int num, int den)
 {
-    int num, den;
     variant v;
-    den = lcd(a.sa[1], b.sa[1]);
-    num = a.sa[0] * lcd / a.sa[1] + b.sa[0] * lcd / b.sa[1];
+    int g = gcd(num, den);
+    num /= g;
+    den /= g;
     assert(num >= SHRT_MIN && num <= SHRT_MAX);
     assert(den >= SHRT_MIN && den <= SHRT_MAX);
     v.sa[0] = (short)num;
@@ -18,19 +41,20 @@ variant frac_add(variant a, variant b)
     return v;
 }
 
+variant frac_add(variant a, variant b)
+{
+    int num, den;
+    den = lcm(a.sa[1], b.sa[1]);
+    num = a.sa[0] * den / a.sa[1] + b.sa[0] * den / b.sa[1];
+    return frac_make(num, den);
+}
+
 variant frac_mul(variant a, variant b)
 {
-    variant v = a;
-    return v;
+    return frac_make(a.sa[0] * b.sa[0], a.sa[1] * b.sa[1]);
 }
 
 variant frac_div(variant a, variant b)
 {
-    variant v = a;
-    return v;
+    return frac_make(a.sa[0] * b.sa[1], a.sa[1] * b.sa[0]);
 }
-
-#ifdef __cplusplus
-}
-#endif
-#endif
diff --git a/src/util/variant.h b/src/util/variant.h
index 8c78bc3ac..f98fa0b80 100644
--- a/src/util/variant.h
+++ b/src/util/variant.h
@@ -21,6 +21,7 @@ extern "C" {
       VAR_FLOAT
   } variant_type;
 
+  variant frac_make(int num, int den);
   variant frac_add(variant a, variant b);
   variant frac_mul(variant a, variant b);
   variant frac_div(variant a, variant b);
diff --git a/src/util/variant.test.c b/src/util/variant.test.c
new file mode 100644
index 000000000..6344e5c33
--- /dev/null
+++ b/src/util/variant.test.c
@@ -0,0 +1,28 @@
+#include <platform.h>
+#include "variant.h"
+
+#include <CuTest.h>
+
+static void test_fractions(CuTest *tc) {
+    variant a, b;
+    a = frac_make(120, 12000);
+    CuAssertIntEquals(tc, 1, a.sa[0]);
+    CuAssertIntEquals(tc, 100, a.sa[1]);
+    b = frac_make(23, 2300);
+    a = frac_add(a, b);
+    CuAssertIntEquals(tc, 1, a.sa[0]);
+    CuAssertIntEquals(tc, 50, a.sa[1]);
+    a = frac_mul(a, b);
+    CuAssertIntEquals(tc, 1, a.sa[0]);
+    CuAssertIntEquals(tc, 5000, a.sa[1]);
+    a = frac_div(b, b);
+    CuAssertIntEquals(tc, 1, a.sa[0]);
+    CuAssertIntEquals(tc, 1, a.sa[1]);
+}
+
+CuSuite *get_variant_suite(void)
+{
+    CuSuite *suite = CuSuiteNew();
+    SUITE_ADD_TEST(suite, test_fractions);
+    return suite;
+}