diff --git a/core/math/bigint/bigint.odin b/core/math/bigint/bigint.odin
index 50934e429..77a1fcb2f 100644
--- a/core/math/bigint/bigint.odin
+++ b/core/math/bigint/bigint.odin
@@ -93,7 +93,8 @@ _MIN_DIGIT_COUNT :: max(3, ((size_of(u128) + _DIGIT_BITS) - 1) / _DIGIT_BITS);
  	- Must be small enough such that `_radix_size` for base 2 does not overflow.
 	`_radix_size` needs two additional bytes for zero termination and sign.
 */
-_MAX_DIGIT_COUNT :: (max(int) - 2) / _DIGIT_BITS;
+_MAX_BIT_COUNT   :: (max(int) - 2);
+_MAX_DIGIT_COUNT :: _MAX_BIT_COUNT / _DIGIT_BITS;
 
 when size_of(rawptr) == 8 {
 	/*
diff --git a/core/math/bigint/example.odin b/core/math/bigint/example.odin
index 38290369d..aded4b3c9 100644
--- a/core/math/bigint/example.odin
+++ b/core/math/bigint/example.odin
@@ -41,48 +41,58 @@ _SQR_TOOM_CUTOFF,
 	fmt.println();
 }
 
+print :: proc(name: string, a: ^Int, base := i8(16)) {
+	as, err := itoa(a, base);
+	defer delete(as);
+
+	if err == .OK {
+		fmt.printf("%v (base: %v, bits used: %v): %v\n", name, base, count_bits(a), as);
+	} else {
+		fmt.printf("%v (error: %v): %v\n", name, err, a);
+	}
+}
+
 demo :: proc() {
-	a,  b,  c: ^Int;
-	as, bs, cs: string;
-	err:  Error;
+	a, b, c: ^Int;
+	err: Error;
 
-	a, err = init();
-	a.digit[2] = 512;
-	a.used = 3;
 	defer destroy(a);
-	as, err = itoa(a, 16);
-	fmt.printf("a: %v, err: %v\n\n", as, err);
-	delete(as);
-
-	b, err = init(42);
 	defer destroy(b);
-	bs, err = itoa(b, 16);
-	fmt.printf("b: %s, err: %v\n\n", bs, err);
-	delete(bs);
+	defer destroy(c);
+
+	a, err = init(1+4+16+64);
+
+	b, err = init(1+2+8+32+128);
 
 	c, err = init(-4);
-	defer destroy(c);
-	cs, err = itoa(c, 16);
-	fmt.printf("c: %s, err: %v\n\n", cs, err);
-	delete(cs);
 
-	// cstr: cstring;
-	// defer delete(cstr);
+	print("a", a, 2);
+	print("b", b, 2);
+	print("c", c, 2);
 
-	// cstr, err = itoa_cstring(a);
-	// fmt.printf("cstring: %v, err: %v\n\n", cstr, err);
+	fmt.println("=== a = a & b ===");
+	err = and(a, a, b);
+	fmt.printf("a &= b error: %v\n", err);
 
-	fmt.println("=== Add ===");
-	err = sub(c, a, b);
+	print("a", a, 2);
+	print("b", b, 10);
 
-	fmt.printf("Error: %v\n", err);
-	as, err = itoa(a, 16);
-	bs, err = itoa(b, 16);
-	cs, err = itoa(c, 16);
-	fmt.printf("a: %v, bits: %v\n", as, count_bits(a));
-	fmt.printf("b: %v, bits: %v\n", bs, count_bits(b));
-	fmt.printf("c: %v, bits: %v\n", cs, count_bits(c));
-	delete(as); delete(bs); delete(cs);
+	fmt.println("\n\n=== b = abs(c) ===");
+	c.sign = .Negative;
+	abs(b, c); // copy c to b.
+
+	print("b", b);
+	print("c", c);
+
+	fmt.println("\n\n=== Set a to (1 << 120) - 1 ===");
+	if err = power_of_two(a, 120); err != .OK {
+		fmt.printf("Error %v while setting a to 1 << 120.\n", err);
+	}
+	if err = sub(a, a, 1); err != .OK {
+		fmt.printf("Error %v while subtracting 1 from a\n", err);	
+	}
+	print("a", a, 16);
+	fmt.println("Expected a to be:        FFFFFFFFFFFFFFFFFFFFFFFFFFFFFF");
 }
 
 main :: proc() {
diff --git a/core/math/bigint/helpers.odin b/core/math/bigint/helpers.odin
index a96eabb2c..ecd9e4968 100644
--- a/core/math/bigint/helpers.odin
+++ b/core/math/bigint/helpers.odin
@@ -102,6 +102,116 @@ set_integer :: proc(a: ^Int, n: $T, minimize := false, loc := #caller_location)
 
 set :: proc{set_integer};
 
+/*
+	Copy one `Int` to another.
+*/
+copy :: proc(dest, src: ^Int, allocator := context.allocator) -> (err: Error) {
+	/*
+		If dest == src, do nothing
+	*/
+	if (dest == src) {
+		return .OK;
+	}
+
+	/*
+		Check they're both initialized.
+	*/
+	if !(is_initialized(dest) && is_initialized(src)) {
+		return .Invalid_Input;
+	}
+
+	/*
+		Grow `dest` to fit `src`.
+	*/
+	if err = grow(dest, min(src.used, _DEFAULT_DIGIT_COUNT)); err != .OK {
+		return err;
+	}
+
+	/*
+		Copy everything over and zero high digits.
+	*/
+	assert(dest.allocated >= src.used);
+	for v, i in src.digit[:src.used+1] {
+		dest.digit[i] = v;
+	}
+	dest.used = src.used;
+	dest.sign = src.sign;
+	_zero_unused(dest);
+	return .OK;
+}
+
+/*
+	Set `dest` to |`src`|.
+*/
+abs_bigint :: proc(dest, src: ^Int) -> (err: Error) {
+	/*
+		If `dest == src`, just fix `dest`'s sign.
+	*/
+	if (dest == src) {
+		dest.sign = .Zero_or_Positive;
+		return .OK;
+	}
+
+	/*
+		Check they're both initialized.
+	*/
+	if !(is_initialized(dest) && is_initialized(src)) {
+		return .Invalid_Input;
+	}
+
+	/*
+		Copy `src` to `dest`
+	*/
+	if err = copy(dest, src); err != .OK {
+		return err;
+	}
+
+	/*
+		Fix sign.
+	*/
+	dest.sign = .Zero_or_Positive;
+	return .OK;
+}
+
+abs_integer :: proc(n: $T) -> T where intrinsics.type_is_integer(T) {
+	return n if n >= 0 else -n;
+}
+abs :: proc{abs_bigint, abs_integer};
+
+/*
+	Set `dest` to `-src`.
+*/
+neg :: proc(dest, src: ^Int) -> (err: Error) {
+	/*
+		If `dest == src`, just fix `dest`'s sign.
+	*/
+	sign := Sign.Negative if !(is_zero(src) && is_neg(src)) else Sign.Zero_or_Positive;
+	if dest == src {
+		dest.sign = sign;
+		return .OK;
+	}
+
+	/*
+		Check they're both initialized.
+	*/
+	if !(is_initialized(dest) && is_initialized(src)) {
+		return .Invalid_Input;
+	}
+
+	/*
+		Copy `src` to `dest`
+	*/
+	if err = copy(dest, src); err != .OK {
+		return err;
+	}
+
+	/*
+		Fix sign.
+	*/
+	dest.sign = sign;
+	return .OK;
+}
+
 /*
 	Helpers to extract values from the `Int`.
 */
@@ -245,6 +355,35 @@ minus_one :: proc(a: ^Int, minimize := false) -> (err: Error) {
 	return .OK;
 }
 
+power_of_two :: proc(a: ^Int, power: int) -> (err: Error) {
+	assert_initialized(a);
+
+	/*
+
+	*/
+	if power < 0 || power > _MAX_BIT_COUNT {
+		return .Invalid_Input;
+	}
+
+	/*
+		Grow to accomodate the single bit.
+	*/
+	a.used = (power / _DIGIT_BITS) + 1;
+	if err = grow(a, a.used); err != .OK {
+		return err;
+	}
+	/*
+		Zero the entirety.
+	*/
+	mem.zero_slice(a.digit[:]);
+
+	/*
+		Set the bit.
+	*/
+	a.digit[power / _DIGIT_BITS] = 1 << uint((power % _DIGIT_BITS));
+   	return .OK;
+}
+
 /*
 	Count bits in an `Int`.
 */
diff --git a/core/math/bigint/logical.odin b/core/math/bigint/logical.odin
new file mode 100644
index 000000000..bd80226eb
--- /dev/null
+++ b/core/math/bigint/logical.odin
@@ -0,0 +1,113 @@
+package bigint
+
+/*
+	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.
+
+	This file contains logical operations like `and`, `or` and `xor`.
+*/
+
+import "core:fmt"
+
+@private
+Operator :: enum u8 {
+	And = 1,
+	Or  = 2,
+	Xor = 3,
+}
+
+/*
+	2's complement `and`, returns `dest = a & b;`
+*/
+
+_binary_op :: proc(dest, a, b: ^Int, op: Operator) -> (err: Error) {
+	assert_initialized(dest); assert_initialized(a); assert_initialized(b);
+
+	used := max(a.used, b.used) + 1;
+	neg: bool;
+
+	switch(op) {
+	case .And:
+		neg  = is_neg(a) && is_neg(b);
+	case .Or:
+		neg  = is_neg(a) || is_neg(b);
+	case .Xor:
+		neg  = is_neg(a) != is_neg(b);
+	case:
+		return .Invalid_Input;
+	}
+
+	ac, bc, cc := DIGIT(1), DIGIT(1), DIGIT(1);
+
+	/*
+		Grow the destination to accomodate the result.
+	*/
+	if err = grow(dest, used); err != .OK {
+		return err;
+	}
+
+	for i := 0; i < used; i += 1 {
+		x, y: DIGIT;
+
+		/*
+			Convert to 2's complement if negative.
+		*/
+		if is_neg(a) {
+			ac += _MASK if i >= a.used else (~a.digit[i] & _MASK);
+			x = ac & _MASK;
+			ac >>= _DIGIT_BITS;
+		} else {
+			x = 0 if i >= a.used else a.digit[i];
+		}
+
+		/*
+			Convert to 2's complement if negative.
+		*/
+		if is_neg(a) {
+			bc += _MASK if i >= b.used else (~b.digit[i] & _MASK);
+			y = bc & _MASK;
+			bc >>= _DIGIT_BITS;
+		} else {
+			y = 0 if i >= b.used else b.digit[i];
+		}
+
+		switch(op) {
+		case .And:
+			dest.digit[i] = x & y;
+		case .Or:
+			dest.digit[i] = x | y;
+		case .Xor:
+			dest.digit[i] = x ~ y;
+		}
+
+		/*
+			Convert to to sign-magnitude if negative.
+		*/
+		if neg {
+			cc += ~dest.digit[i] & _MASK;
+			dest.digit[i] = cc & _MASK;
+			cc >>= _DIGIT_BITS;
+		}
+	}
+
+	dest.used = used;
+	dest.sign = .Negative if neg else .Zero_or_Positive;
+	clamp(dest);
+	return .OK;
+}
+
+and :: proc(dest, a, b: ^Int) -> (err: Error) {
+	return _binary_op(dest, a, b, .And);
+}
+
+or  :: proc(dest, a, b: ^Int) -> (err: Error) {
+	return _binary_op(dest, a, b, .Or);
+}
+
+xor :: proc(dest, a, b: ^Int) -> (err: Error) {
+	return _binary_op(dest, a, b, .Xor);
+}