core:math/bits: Add docs + tests for rotate_left* and log2

2026-07-30 03:10:06 +00:00 · 2025-10-14 23:30:38 +02:00
parent 225edc552a
commit 347eae3a66
3 changed files with 318 additions and 10 deletions
@@ -0,0 +1,148 @@
+package test_core_math_bits
+
+import "core:math/bits"
+import "core:testing"
+
+@test
+test_log2 :: proc(t: ^testing.T) {
+	dumb_log2 :: proc(x: $T) -> (res: T) {
+		N :: T(size_of(T) * 8)
+
+		if x == 0 {
+			return max(T)
+		}
+
+		for k := N - 1; k > 0; k -= 1 {
+			bit_pos := T(k)
+			if (x >> bit_pos) & 1 == 1 {
+				return bit_pos
+			}
+		}
+		return
+	}
+
+	testing.expect_value(t, bits.log2(  u8(0)), max(u8))
+	testing.expect_value(t, bits.log2( u16(0)), max(u16))
+	testing.expect_value(t, bits.log2( u32(0)), max(u32))
+	testing.expect_value(t, bits.log2( u64(0)), max(u64))
+	testing.expect_value(t, bits.log2(uint(0)), max(uint))
+
+	for x in u8(0)..<max(u8) {
+		l1 := bits.log2(x)
+		l2 := dumb_log2(x)
+		testing.expectf(t, l1 == l2, "bits.log({0}): {1}, dumb_log2({0}): {2}", x, l1, l2)
+	}
+
+	for x in u16(0)..<max(u16) {
+		l1 := bits.log2(x)
+		l2 := dumb_log2(x)
+		testing.expectf(t, l1 == l2, "bits.log({0}): {1}, dumb_log2({0}): {2}", x, l1, l2)
+	}
+
+	// Takes too long to run this with 32+ integers, and if it works with u8 and u16, it'll work with u32, u64, etc. as well.
+}
+
+@test
+test_rotate :: proc(t: ^testing.T) {
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, 0), 0b0000_1101)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, 1), 0b0001_1010)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, 2), 0b0011_0100)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, 3), 0b0110_1000)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, 4), 0b1101_0000)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, 5), 0b1010_0001)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, 6), 0b0100_0011)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, 7), 0b1000_0110)
+
+	{
+		// 8 single bit rotations should result in the original number
+		r := u8(0b1101)
+		for _ in 1..=8 {
+			r = bits.rotate_left8(r, 1)
+		}
+		testing.expect_value(t, r, 0b1101)
+	}
+	{
+		// 16 single bit rotations should result in the original number
+		r := u16(0b1101)
+		for _ in 1..=16 {
+			r = bits.rotate_left16(r, 1)
+		}
+		testing.expect_value(t, r, 0b1101)
+	}
+	{
+		// 32 single bit rotations should result in the original number
+		r := u32(0b1101)
+		for _ in 1..=32 {
+			r = bits.rotate_left32(r, 1)
+		}
+		testing.expect_value(t, r, 0b1101)
+	}
+	{
+		// 64 single bit rotations should result in the original number
+		r := u64(0b1101)
+		for _ in 1..=64 {
+			r = bits.rotate_left64(r, 1)
+		}
+		testing.expect_value(t, r, 0b1101)
+	}
+	{
+		// `size_of(uint) * 8` single bit rotations should result in the original number
+		r := uint(0b1101)
+		for _ in 1..=(size_of(uint) * 8) {
+			r = bits.rotate_left(r, 1)
+		}
+		testing.expect_value(t, r, 0b1101)
+	}
+
+	// rotate right = rotate left by negative amount
+
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, -0), 0b0000_1101)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, -1), 0b1000_0110)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, -2), 0b0100_0011)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, -3), 0b1010_0001)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, -4), 0b1101_0000)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, -5), 0b0110_1000)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, -6), 0b0011_0100)
+	testing.expect_value(t, bits.rotate_left8(0b0000_1101, -7), 0b0001_1010)
+
+	{
+		// 8 single bit rotations should result in the original number
+		r := u8(0b1101)
+		for _ in 1..=8 {
+			r = bits.rotate_left8(r, -1)
+		}
+		testing.expect_value(t, r, 0b1101)
+	}
+	{
+		// 16 single bit rotations should result in the original number
+		r := u16(0b1101)
+		for _ in 1..=16 {
+			r = bits.rotate_left16(r, -1)
+		}
+		testing.expect_value(t, r, 0b1101)
+	}
+	{
+		// 32 single bit rotations should result in the original number
+		r := u32(0b1101)
+		for _ in 1..=32 {
+			r = bits.rotate_left32(r, -1)
+		}
+		testing.expect_value(t, r, 0b1101)
+	}
+	{
+		// 64 single bit rotations should result in the original number
+		r := u64(0b1101)
+		for _ in 1..=64 {
+			r = bits.rotate_left64(r, -1)
+		}
+		testing.expect_value(t, r, 0b1101)
+	}
+	{
+		// `size_of(uint) * 8` single bit rotations should result in the original number
+		r := uint(0b1101)
+		for _ in 1..=(size_of(uint) * 8) {
+			r = bits.rotate_left(r, -1)
+		}
+		testing.expect_value(t, r, 0b1101)
+	}
+}