zig/std/special/builtin.zig

// These functions are provided when not linking against libc because LLVM
// sometimes generates code that calls them.

// Note that these functions do not return `dest`, like the libc API.
// The semantics of these functions is dictated by the corresponding
// LLVM intrinsics, not by the libc API.

export fn memset(dest: ?&u8, c: u8, n: usize) {
    @setDebugSafety(this, false);

    if (n == 0)
        return;

    const d = ??dest;
    var index: usize = 0;
    while (index != n; index += 1)
        d[index] = c;
}

export fn memcpy(noalias dest: ?&u8, noalias src: ?&const u8, n: usize) {
    @setDebugSafety(this, false);

    if (n == 0)
        return;

    const d = ??dest;
    const s = ??src;
    var index: usize = 0;
    while (index != n; index += 1)
        d[index] = s[index];
}

// Avoid dragging in the debug safety mechanisms into this .o file.
pub fn panic(message: []const u8) -> noreturn {
    unreachable;
}