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// SPDX-License-Identifier: MIT
// Copyright (c) 2015-2021 Zig Contributors
// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
// The MIT license requires this copyright notice to be included in all copies
// and substantial portions of the software.
const builtin = @import("builtin");
const is_test = builtin.is_test;
const std = @import("std");
const maxInt = std.math.maxInt;
const FLT_MANT_DIG = 24;
pub fn __floatuntisf(arg: u128) callconv(.C) f32 {
@setRuntimeSafety(is_test);
if (arg == 0)
return 0.0;
var a = arg;
const N: u32 = @sizeOf(u128) * 8;
const sd = @bitCast(i32, N - @clz(u128, a)); // number of significant digits
var e: i32 = sd - 1; // exponent
if (sd > FLT_MANT_DIG) {
// start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
// finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
// 12345678901234567890123456
// 1 = msb 1 bit
// P = bit FLT_MANT_DIG-1 bits to the right of 1
// Q = bit FLT_MANT_DIG bits to the right of 1
// R = "or" of all bits to the right of Q
switch (sd) {
FLT_MANT_DIG + 1 => {
a <<= 1;
},
FLT_MANT_DIG + 2 => {},
else => {
const shift_amt = @bitCast(i32, N + (FLT_MANT_DIG + 2)) - sd;
const shift_amt_u7 = @intCast(u7, shift_amt);
a = (a >> @intCast(u7, sd - (FLT_MANT_DIG + 2))) |
@boolToInt((a & (@as(u128, maxInt(u128)) >> shift_amt_u7)) != 0);
},
}
// finish
a |= @boolToInt((a & 4) != 0); // Or P into R
a += 1; // round - this step may add a significant bit
a >>= 2; // dump Q and R
// a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits
if ((a & (@as(u128, 1) << FLT_MANT_DIG)) != 0) {
a >>= 1;
e += 1;
}
// a is now rounded to FLT_MANT_DIG bits
} else {
a <<= @intCast(u7, FLT_MANT_DIG - sd);
// a is now rounded to FLT_MANT_DIG bits
}
const high = @bitCast(u32, (e + 127) << 23); // exponent
const low = @truncate(u32, a) & 0x007fffff; // mantissa
return @bitCast(f32, high | low);
}
test "import floatuntisf" {
_ = @import("floatuntisf_test.zig");
}
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