bigint: Working on itoa and logn.

core/math/bigint/log.odin

@@ -0,0 +1,46 @@
+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.
+*/
+
+log_n :: proc(a: ^Int, base: int) -> (log: int, err: Error) {
+	assert_initialized(a);
+	if is_neg(a) || is_zero(a) || base < 2 || DIGIT(base) > _DIGIT_MAX {
+		return -1, .Invalid_Input;
+	}
+
+	if is_power_of_two(base) {
+		return _log_power_of_two(a, base), .OK;
+	}
+
+   // if (MP_HAS(S_MP_LOG_D) && (a->used == 1)) {
+   //    *c = s_mp_log_d((mp_digit)base, a->dp[0]);
+   //    return MP_OKAY;
+   // }
+
+   // if (MP_HAS(S_MP_LOG)) {
+   //    return s_mp_log(a, (mp_digit)base, c);
+   // }
+
+	return -1, .Unimplemented;
+}
+
+/*
+	Returns the log2 of an `Int`, provided `base` is a power of two.
+	Don't call it if it isn't.
+*/
+_log_power_of_two :: proc(a: ^Int, base: int) -> (log: int) {
+	base := base;
+	y: int;
+	for y = 0; base & 1 == 0; {
+		y += 1;
+		base >>= 1;
+	}
+	return (count_bits(a) - 1) / y;
+}