Fix core:math/fixed.

core/math/fixed/fixed.odin

@@ -41,7 +41,7 @@ init_from_f64 :: proc(x: ^$T/Fixed($Backing, $Fraction_Width), val: f64) {
 init_from_parts :: proc(x: ^$T/Fixed($Backing, $Fraction_Width), integer, fraction: Backing) {
 	x.i  = fraction
 	x.i &= 1<<Fraction_Width - 1
-	x.i |= integer
+	x.i |= (integer << Fraction_Width)
 }
 
 to_f64 :: proc(x: $T/Fixed($Backing, $Fraction_Width)) -> f64 {

tests/core/math/fixed/test_core_math_fixed.odin

@@ -0,0 +1,51 @@
+package test_core_math_fixed
+
+import "core:math/fixed"
+import "core:testing"
+
+@test
+test_fixed_4_4_unsigned :: proc(t: ^testing.T) {
+	I_SHIFT :: 4
+	F_MASK  :: 15
+	F_ULP   :: 0.0625
+	Fixed   :: fixed.Fixed(u8, 4)
+
+	for c in 0..<256 {
+		raw := u8(c)
+		fv  := transmute(Fixed)raw
+
+		i := raw >> I_SHIFT
+		f := raw &  F_MASK
+		expected := f64(i) + F_ULP * f64(f)
+
+		testing.expectf(t, fixed.to_f64(fv) == expected, "Expected Fixed(u8, 4)(%v) to equal %.5f, got %.5f", raw, expected, fixed.to_f64(fv))
+	}
+}
+
+@test
+test_fixed_4_4_signed :: proc(t: ^testing.T) {
+	I_SHIFT :: 4
+	F_MASK  :: 15
+	F_ULP   :: 0.0625
+	Fixed   :: fixed.Fixed(i8, 4)
+
+	for c in 0..<256 {
+		raw := i8(c)
+		fv  := transmute(Fixed)raw
+
+		f := raw & F_MASK
+		expected: f64
+		if c < 128 {
+			i := raw >> I_SHIFT
+			expected = f64(i) + F_ULP * f64(f)
+		} else if c == 128 {
+			expected = 8.0
+
+		} else if c > 128 {
+			i := i8(-8)
+			i += (raw & 0b0111_0000) >> I_SHIFT
+			expected = f64(i) + F_ULP * f64(f)
+		}
+		testing.expectf(t, fixed.to_f64(fv) == expected, "Expected Fixed(i8, 4)(%v, %v) to equal %.5f, got %.5f", c, raw, expected, fixed.to_f64(fv))
+	}
+}