added multiplication

README.md

@@ -13,7 +13,8 @@ Don't. The makefile only includes a test target, because I want to test my code.
 silly silly_zeros(); // creates a fixed point value of zero
 
 silly silly_add(silly, silly); // addition
-silly silly_sub(silly, silly); // subtracttion
+silly silly_sub(silly, silly); // subtraction
+silly silly_mul(silly, silly); // multiplication
 
 char* silly_to_string(silly); // converts a fixed point value to a string (memory is now yours)
 ```

silly.c

@@ -24,7 +24,7 @@ silly silly_add(silly x, silly y) {
   z.before = x.before + y.before;
   z.after = x.after + y.after;
 
-  if (z.after < x.after && z.after < y.after) z.before += 1;
+  if (z.after < x.after && z.after < y.after) z.before++;
   return z;
 }
 
@@ -53,7 +53,26 @@ silly silly_sub(silly x, silly y) {
 
   z.after = x.after - y.after;
 
-  if (z.after > x.after) z.before -= 1;
+  if (z.after > x.after) z.before--;
+
+  return z;
+}
+
+silly silly_mul(silly x, silly y) {
+  silly z = silly_zeros();
+
+  z.sign = x.sign ^ y.sign;
+
+  uint64_t t0 = (x.before * y.after);
+  uint64_t t1 = (y.before * x.after);
+  z.before = x.before * y.before + (t0>>32) + (t1>>32);
+  uint32_t t0b = t0&0xffffffff;
+  uint32_t t1b = t1&0xffffffff;
+  uint32_t tsum = t0b + t1b;
+  if (tsum < t0b || tsum < t1b) z.before++;
+  z.after = x.after * y.after + tsum;
+
+  if (z.after < tsum) z.before++;
 
   return z;
 }

silly.h

@@ -12,6 +12,7 @@ silly silly_zeros();
 
 silly silly_add(silly, silly);
 silly silly_sub(silly, silly);
+silly silly_mul(silly, silly);
 
 //silly silly_from_8(float8_t);
 //silly silly_from_16(float16_t);

tests/test.c

@@ -67,11 +67,37 @@ TEST silly_subtraction() {
   PASS();
 }
 
+TEST silly_multiplication() {
+  silly x = silly_zeros();
+  x.sign = 1;
+  x.before = 3;
+  silly y = silly_zeros();
+  y.before = 2;
+  x = silly_mul(x, y);
+
+  ASSERT_EQ_FMT(1, x.sign, "%d");
+  ASSERT_EQ_FMT(6, x.before, "%d");
+  ASSERT_EQ_FMT(0, x.after, "%d");
+
+  x = silly_zeros();
+  x.before = 3;
+  x.after = 0xffffffff;
+  y = silly_zeros();
+  y.before = 2;
+  x = silly_mul(x, y);
+
+  ASSERT_EQ_FMT(7, x.before, "%d");
+  ASSERT_EQ_FMT(0, x.after, "%d");
+
+  PASS();
+}
+
 SUITE(tests) {
     RUN_TEST(silly_zeros_is_zero);
     RUN_TEST(silly_string);
     RUN_TEST(silly_addition);
     RUN_TEST(silly_subtraction);
+    RUN_TEST(silly_multiplication);
 }
 
 GREATEST_MAIN_DEFS();