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less_than_5

log10.less_than_5

inline fn less_than_5(x: u32) u32

File

lib/std/math/log10.zig:118

Code

inline fn less_than_5(x: u32) u32 {
    // Similar to log10u8, when adding one of these constants to val,
    // we get two possible bit patterns above the low 17 bits,
    // depending on whether val is below or above the threshold.
    const C1: u32 = 0b011_00000000000000000 - 10; // 393206
    const C2: u32 = 0b100_00000000000000000 - 100; // 524188
    const C3: u32 = 0b111_00000000000000000 - 1000; // 916504
    const C4: u32 = 0b100_00000000000000000 - 10000; // 514288

    // Value of top bits:
    //                +c1  +c2  1&2  +c3  +c4  3&4   ^
    //         0..=9  010  011  010  110  011  010  000 = 0
    //       10..=99  011  011  011  110  011  010  001 = 1
    //     100..=999  011  100  000  110  011  010  010 = 2
    //   1000..=9999  011  100  000  111  011  011  011 = 3
    // 10000..=99999  011  100  000  111  100  100  100 = 4
    return (((x + C1) & (x + C2)) ^ ((x + C3) & (x + C4))) >> 17;
}