chore(cpu): iron out some false assumptions

src/util.zig

@@ -1,6 +1,30 @@
 const std = @import("std");
+const assert = std.debug.assert;
 
-pub fn u32_sign_extend(value: u32, bitSize: anytype) u32 {
-    const amount: u5 = 32 - bitSize;
-    return @bitCast(u32, @bitCast(i32, value << amount) >> amount);
+pub fn signExtend(comptime T: type, comptime bits: usize, value: anytype) T {
+    const ValT = comptime @TypeOf(value);
+    comptime assert(isInteger(ValT));
+    comptime assert(isSigned(ValT));
+
+    const value_bits = @typeInfo(ValT).Int.bits;
+    comptime assert(value_bits >= bits);
+
+    const bit_diff = value_bits - bits;
+
+    // (1 << bits) -1 is a mask that will take values like 0x100 and make them 0xFF
+    // value & mask so that only the relevant bits are sign extended
+    // therefore, value & ((1 << bits) - 1) is the isolation of the relevant bits
+    return ((value & ((1 << bits) - 1)) << bit_diff) >> bit_diff;
+}
+
+pub fn u32SignExtend(comptime bits: usize, value: u32) u32 {
+    return @bitCast(u32, signExtend(i32, bits, @bitCast(i32, value)));
+}
+
+fn isInteger(comptime T: type) bool {
+    return @typeInfo(T) == .Int;
+}
+
+fn isSigned(comptime T: type) bool {
+    return @typeInfo(T).Int.signedness == .signed;
 }