Commit c5d359e4cdcc6090f0ff1803adb929247027e7cb | zig

author	Guillaume Wenzek <gwenzek@users.noreply.github.com> 2024-01-12 17:28:56+01:00
committer	Andrew Kelley <andrew@ziglang.org> 2024-01-13 18:46:16-08:00
log	c5d359e4cdcc6090f0ff1803adb929247027e7cb
tree	637055ee759a05603fad17d3cced1c1fdb84e0d7
parent	d55d1e32b65dd829cec17b5c5d65db10608d097c

3 files changed, 19 insertions(+), 6 deletions(-)

lib/std/math.zig+2

...	...	@@ -672,6 +672,7 @@ test "rotl" {
672	672	/// - 1. Suitable for 0-based bit indices of T.
673	673	pub fn Log2Int(comptime T: type) type {
674	674	// comptime ceil log2
	675	if (T == comptime_int) return comptime_int;
675	676	comptime var count = 0;
676	677	comptime var s = @typeInfo(T).Int.bits - 1;
677	678	inline while (s != 0) : (s >>= 1) {
...	...	@@ -684,6 +685,7 @@ pub fn Log2Int(comptime T: type) type {
684	685	/// Returns an unsigned int type that can hold the number of bits in T.
685	686	pub fn Log2IntCeil(comptime T: type) type {
686	687	// comptime ceil log2
	688	if (T == comptime_int) return comptime_int;
687	689	comptime var count = 0;
688	690	comptime var s = @typeInfo(T).Int.bits;
689	691	inline while (s != 0) : (s >>= 1) {

lib/std/math/log.zig+1-4

...	...	@@ -24,11 +24,8 @@ pub fn log(comptime T: type, base: T, x: T) T {
24	24	return @as(comptime_float, @log(@as(f64, x)) / @log(float_base));
25	25	},
26	26
27		// TODO: implement integer log without using float math.
28		// The present implementation is incorrect, for example
29		// `log(comptime_int, 9, 59049)` should return `5` and not `4`.
30	27	.ComptimeInt => {
31		return @as(comptime_int, @floor(@log(@as(f64, x)) / @log(float_base)));
	28	return @as(comptime_int, math.log_int(comptime_int, base, x));
32	29	},
33	30
34	31	.Int => \|IntType\| switch (IntType.signedness) {

lib/std/math/log_int.zig+16-2

...	...	@@ -7,10 +7,15 @@ const Log2Int = math.Log2Int;
7	7	/// Returns the logarithm of `x` for the provided `base`, rounding down to the nearest integer.
8	8	/// Asserts that `base > 1` and `x > 0`.
9	9	pub fn log_int(comptime T: type, base: T, x: T) Log2Int(T) {
10		if (@typeInfo(T) != .Int or @typeInfo(T).Int.signedness != .unsigned)
11		@compileError("log_int requires an unsigned integer, found " ++ @typeName(T));
	10	const valid = switch (@typeInfo(T)) {
	11	.ComptimeInt => true,
	12	.Int => \|IntType\| IntType.signedness == .unsigned,
	13	else => false,
	14	};
	15	if (!valid) @compileError("log_int requires an unsigned integer, found " ++ @typeName(T));
12	16
13	17	assert(base > 1 and x > 0);
	18	if (base == 2) return math.log2_int(T, x);
14	19
15	20	// Let's denote by [y] the integer part of y.
16	21
...	...	@@ -112,3 +117,12 @@ test "math.log_int vs math.log10" {
112	117	}
113	118	}
114	119	}
	120
	121	test "math.log_int at comptime" {
	122	const x = 59049; // 9 ** 5;
	123	comptime {
	124	if (math.log_int(comptime_int, 9, x) != 5) {
	125	@compileError("log(9, 59049) should be 5");
	126	}
	127	}
	128	}