Zig 0.17.0-dev (Split by item)

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dd_mul128

Compute a*b exactly, returning the exact result in a struct dd. We assume that both a and b are normalized, so no underflow or overflow will occur. The current rounding mode must be round-to-nearest.

fma.dd_mul128

fn dd_mul128(a: f128, b: f128) dd128

File

lib/compiler_rt/fma.zig:294

Code

fn dd_mul128(a: f128, b: f128) dd128 {
    var ret: dd128 = undefined;
    const split: f128 = 0x1.0p57 + 1.0;

    var p = a * split;
    var ha = a - p;
    ha += p;
    const la = a - ha;

    p = b * split;
    var hb = b - p;
    hb += p;
    const lb = b - hb;

    p = ha * hb;
    const q = ha * lb + la * hb;

    ret.hi = p + q;
    ret.lo = p - ret.hi + q + la * lb;
    return ret;
}