1 /// These functions compute the integer logarithm of their type, assuming
2 /// that someone has already checked that the value is strictly positive.
6 pub const fn u8(val: u8) -> u32 {
9 // For better performance, avoid branches by assembling the solution
10 // in the bits above the low 8 bits.
12 // Adding c1 to val gives 10 in the top bits for val < 10, 11 for val >= 10
13 const C1: u32 = 0b11_00000000 - 10; // 758
14 // Adding c2 to val gives 01 in the top bits for val < 100, 10 for val >= 100
15 const C2: u32 = 0b10_00000000 - 100; // 412
20 // 10..=99 11 01 01 = 1
21 // 100..=255 11 10 10 = 2
22 ((val + C1) & (val + C2)) >> 8
27 const fn less_than_5(val: u32) -> u32 {
28 // Similar to u8, when adding one of these constants to val,
29 // we get two possible bit patterns above the low 17 bits,
30 // depending on whether val is below or above the threshold.
31 const C1: u32 = 0b011_00000000000000000 - 10; // 393206
32 const C2: u32 = 0b100_00000000000000000 - 100; // 524188
33 const C3: u32 = 0b111_00000000000000000 - 1000; // 916504
34 const C4: u32 = 0b100_00000000000000000 - 10000; // 514288
37 // +c1 +c2 1&2 +c3 +c4 3&4 ^
38 // 0..=9 010 011 010 110 011 010 000 = 0
39 // 10..=99 011 011 011 110 011 010 001 = 1
40 // 100..=999 011 100 000 110 011 010 010 = 2
41 // 1000..=9999 011 100 000 111 011 011 011 = 3
42 // 10000..=99999 011 100 000 111 100 100 100 = 4
43 (((val + C1) & (val + C2)) ^ ((val + C3) & (val + C4))) >> 17
46 // 0 < val <= u16::MAX
48 pub const fn u16(val: u16) -> u32 {
49 less_than_5(val as u32)
52 // 0 < val <= u32::MAX
54 pub const fn u32(mut val: u32) -> u32 {
60 log + less_than_5(val)
63 // 0 < val <= u64::MAX
65 pub const fn u64(mut val: u64) -> u32 {
67 if val >= 10_000_000_000 {
68 val /= 10_000_000_000;
75 log + less_than_5(val as u32)
78 // 0 < val <= u128::MAX
80 pub const fn u128(mut val: u128) -> u32 {
82 if val >= 100_000_000_000_000_000_000_000_000_000_000 {
83 val /= 100_000_000_000_000_000_000_000_000_000_000;
85 return log + u32(val as u32);
87 if val >= 10_000_000_000_000_000 {
88 val /= 10_000_000_000_000_000;
94 #[cfg(target_pointer_width = "16")]
96 pub const fn usize(val: usize) -> u32 {
100 #[cfg(target_pointer_width = "32")]
102 pub const fn usize(val: usize) -> u32 {
106 #[cfg(target_pointer_width = "64")]
108 pub const fn usize(val: usize) -> u32 {
112 // 0 < val <= i8::MAX
114 pub const fn i8(val: i8) -> u32 {
118 // 0 < val <= i16::MAX
120 pub const fn i16(val: i16) -> u32 {
124 // 0 < val <= i32::MAX
126 pub const fn i32(val: i32) -> u32 {
130 // 0 < val <= i64::MAX
132 pub const fn i64(val: i64) -> u32 {
136 // 0 < val <= i128::MAX
138 pub const fn i128(val: i128) -> u32 {