big: Add `ilog2`.

core/math/big/example.odin

@@ -213,16 +213,6 @@ int_to_byte_little :: proc(v: ^Int) {
 demo :: proc() {
 	a, b, c, d, e, f, res := &Int{}, &Int{}, &Int{}, &Int{}, &Int{}, &Int{}, &Int{};
 	defer destroy(a, b, c, d, e, f, res);
-
-	set(a, 42);
-	set(b, 6);
-	set(c, 131);
-
-	if err := internal_int_exponent_mod(res, a, b, c); err != nil {
-		fmt.printf("Error: %v\n", err);
-	}
-
-	print("res: ", res);
 }
 
 main :: proc() {

core/math/big/private.odin

@@ -1437,7 +1437,7 @@ _private_int_factorial_binary_split :: proc(res: ^Int, n: int, allocator := cont
 	internal_one(inner, false)                                       or_return;
 	internal_one(outer, false)                                       or_return;
 
-	bits_used := int(_DIGIT_TYPE_BITS - intrinsics.count_leading_zeros(n));
+	bits_used := ilog2(n);
 
 	for i := bits_used; i >= 0; i -= 1 {
 		start := (n >> (uint(i) + 1)) + 1 | 1;

core/math/big/public.odin

@@ -10,6 +10,8 @@
 */
 package math_big
 
+import "core:intrinsics"
+
 /*
 	===========================
 		User-level routines    
@@ -383,6 +385,10 @@ digit_log :: proc(a: DIGIT, base: DIGIT) -> (log: int, err: Error) {
 }
 log :: proc { int_log, digit_log, };
 
+ilog2 :: proc(value: $T) -> (log2: T) {
+	return (size_of(T) * 8) - intrinsics.count_leading_zeros(value);
+}
+
 /*
 	Calculate `dest = base^power` using a square-multiply algorithm.
 */