bigint: refactor to big.Int instead of bigint.Int.

core/math/big/compare.odin

@@ -0,0 +1,155 @@
+package big
+
+/*
+	Copyright 2021 Jeroen van Rijn <nom@duclavier.com>.
+	Made available under Odin's BSD-2 license.
+
+	A BigInt implementation in Odin.
+	For the theoretical underpinnings, see Knuth's The Art of Computer Programming, Volume 2, section 4.3.
+	The code started out as an idiomatic source port of libTomMath, which is in the public domain, with thanks.
+*/
+
+import "core:intrinsics"
+
+is_initialized :: proc(a: ^Int) -> bool {
+	return a != rawptr(uintptr(0));
+}
+
+is_zero :: proc(a: ^Int) -> bool {
+	return is_initialized(a) && a.used == 0;
+}
+
+is_positive :: proc(a: ^Int) -> bool {
+	return is_initialized(a) && a.sign == .Zero_or_Positive;
+}
+is_pos :: is_positive;;
+
+is_negative :: proc(a: ^Int) -> bool {
+	return is_initialized(a) && a.sign == .Negative;
+}
+is_neg :: is_negative;
+
+is_even :: proc(a: ^Int) -> bool {
+	if is_initialized(a) {
+		if is_zero(a) {
+			return true;
+		}
+		if a.used > 0 && a.digit[0] & 1 == 0 {
+			return true;
+		}
+	}
+	return false;
+}
+
+is_odd :: proc(a: ^Int) -> bool {
+	if is_initialized(a) {
+		return !is_even(a);
+	}
+	return false;
+}
+
+is_power_of_two_small :: proc(a: int) -> bool {
+	return ((a) != 0) && (((a) & ((a) - 1)) == 0);
+}
+
+is_power_of_two_large :: proc(a: ^Int) -> (res: bool) {
+	/*
+		Early out for Int == 0.
+	*/
+	if a.used == 0 {
+		return false;
+	}
+
+	/*
+		For an `Int` to be a power of two, its top limb has to be a power of two.
+	*/
+	if !is_power_of_two_small(int(a.digit[a.used - 1])) {
+		return false;
+	}
+
+	/*
+		That was the only limb, so it's a power of two.
+	*/
+	if a.used == 1 {
+		return true;
+	}
+
+	/*
+		For an Int to be a power of two, all limbs except the top one have to be zero.
+	*/
+	for i := 1; i < a.used; i += 1 {
+		if a.digit[i - 1] != 0 {
+			return false;
+		}
+	}
+	return true;
+}
+is_power_of_two :: proc{is_power_of_two_small, is_power_of_two_large};
+
+/*
+	Compare two `Int`s, signed.
+*/
+compare :: proc(a, b: ^Int) -> Comparison_Flag {
+	if !is_initialized(a) { return .Uninitialized; }
+	if !is_initialized(b) { return .Uninitialized; }
+
+	/* Compare based on sign */
+	if a.sign != b.sign {
+		return .Less_Than if is_negative(a) else .Greater_Than;
+	}
+
+	x, y := a, b;
+	/* If negative, compare in the opposite direction */
+	if is_neg(a) {
+		x, y = b, a;
+	}
+	return cmp_mag(x, y);
+}
+cmp :: compare;
+
+/*
+	Compare the magnitude of two `Int`s, unsigned.
+*/
+compare_magnitude :: proc(a, b: ^Int) -> Comparison_Flag {
+	if !is_initialized(a) { return .Uninitialized; }
+	if !is_initialized(b) { return .Uninitialized; }
+
+	/* Compare based on used digits */
+	if a.used != b.used {
+		return .Greater_Than if a.used > b.used else .Less_Than;
+	}
+
+	/* Same number of used digits, compare based on their value */
+	for n := a.used - 1; n >= 0; n -= 1 {
+		if a.digit[n] != b.digit[n] {
+			return .Greater_Than if a.digit[n] > b.digit[n] else .Less_Than;
+		}
+	}
+
+   	return .Equal;
+}
+cmp_mag :: compare_magnitude;
+
+/*
+	Compare an `Int` to an unsigned number upto the size of the backing type.
+*/
+compare_digit :: proc(a: ^Int, u: DIGIT) -> Comparison_Flag {
+	if !is_initialized(a) { return .Uninitialized; }
+
+	/* Compare based on sign */
+	if is_neg(a) {
+		return .Less_Than;
+	}
+
+	/* Compare based on magnitude */
+	if a.used > 1 {
+		return .Greater_Than;
+	}
+
+	/* Compare the only digit in `a` to `u`. */
+	if a.digit[0] != u {
+		return .Greater_Than if a.digit[0] > u else .Less_Than;
+	}
+
+	return .Equal;
+}