zig/lib/compiler_rt/divmodei4.zig

const builtin = @import("builtin");
const endian = builtin.cpu.arch.endian();

const std = @import("std");

const compiler_rt = @import("../compiler_rt.zig");
const udivmod = @import("udivmodei4.zig").divmod;
const symbol = @import("../compiler_rt.zig").symbol;

comptime {
    symbol(&__divei4, "__divei4");
    symbol(&__modei4, "__modei4");
}

inline fn limb(x: []u32, i: usize) *u32 {
    return if (endian == .little) &x[i] else &x[x.len - 1 - i];
}

inline fn neg(x: []u32) void {
    var ov: u1 = 1;
    for (0..x.len) |limb_index| {
        const l = limb(x, limb_index);
        l.*, ov = @addWithOverflow(~l.*, ov);
    }
}

const max_limbs = std.math.divCeil(usize, 65535, 32) catch unreachable;

fn divmod(q: ?[]u32, r: ?[]u32, u: []const u32, v: []const u32) !void {
    const u_sign: i32 = @bitCast(u[u.len - 1]);
    const v_sign: i32 = @bitCast(v[v.len - 1]);
    var ua: [max_limbs]u32 = undefined;
    const us = ua[0..u.len];
    @memcpy(us, u);
    var va: [max_limbs]u32 = undefined;
    const vs = va[0..v.len];
    @memcpy(vs, v);
    if (u_sign < 0) neg(us);
    if (v_sign < 0) neg(vs);
    try @call(.always_inline, udivmod, .{ q, r, us, vs });
    if (q) |x| if (u_sign ^ v_sign < 0) neg(x);
    if (r) |x| if (u_sign < 0) neg(x);
}

pub fn __divei4(q_p: [*]u8, u_p: [*]const u8, v_p: [*]const u8, bits: usize) callconv(.c) void {
    @setRuntimeSafety(compiler_rt.test_safety);
    const byte_size = std.zig.target.intByteSize(&builtin.target, @intCast(bits));
    const q: []u32 = @ptrCast(@alignCast(q_p[0..byte_size]));
    const u: []const u32 = @ptrCast(@alignCast(u_p[0..byte_size]));
    const v: []const u32 = @ptrCast(@alignCast(v_p[0..byte_size]));
    @call(.always_inline, divmod, .{ q, null, u, v }) catch unreachable;
}

pub fn __modei4(r_p: [*]u8, u_p: [*]u8, v_p: [*]u8, bits: usize) callconv(.c) void {
    @setRuntimeSafety(compiler_rt.test_safety);
    const byte_size = std.zig.target.intByteSize(&builtin.target, @intCast(bits));
    const r: []u32 = @ptrCast(@alignCast(r_p[0..byte_size]));
    const u: []u32 = @ptrCast(@alignCast(u_p[0..byte_size]));
    const v: []u32 = @ptrCast(@alignCast(v_p[0..byte_size]));
    @call(.always_inline, divmod, .{ null, r, u, v }) catch unreachable;
}