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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 std = @import("std");
const maxInt = std.math.maxInt;
const FLT_MANT_DIG = 24;
pub fn __floatundisf(arg: u64) callconv(.C) f32 {
@setRuntimeSafety(builtin.is_test);
if (arg == 0) return 0;
var a = arg;
const N: usize = @typeInfo(@TypeOf(a)).Int.bits;
// Number of significant digits
const sd = N - @clz(u64, a);
// 8 exponent
var e = @intCast(u32, sd) - 1;
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 = @intCast(u6, ((N + FLT_MANT_DIG + 2) - sd));
const all_ones: u64 = maxInt(u64);
a = (a >> @intCast(u6, sd - (FLT_MANT_DIG + 2))) |
@boolToInt(a & (all_ones >> shift_amt) != 0);
},
}
// Or P into R
a |= @boolToInt((a & 4) != 0);
// round - this step may add a significant bit
a += 1;
// dump Q and R
a >>= 2;
// a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits
if ((a & (@as(u64, 1) << FLT_MANT_DIG)) != 0) {
a >>= 1;
e += 1;
}
// a is now rounded to FLT_MANT_DIG bits
} else {
a <<= @intCast(u6, FLT_MANT_DIG - sd);
// a is now rounded to FLT_MANT_DIG bits
}
const result: u32 = ((e + 127) << 23) | // exponent
@truncate(u32, a & 0x007FFFFF); // mantissa
return @bitCast(f32, result);
}
pub fn __aeabi_ul2f(arg: u64) callconv(.AAPCS) f32 {
@setRuntimeSafety(false);
return @call(.{ .modifier = .always_inline }, __floatundisf, .{arg});
}
fn test__floatundisf(a: u64, expected: f32) void {
std.testing.expectEqual(expected, __floatundisf(a));
}
test "floatundisf" {
test__floatundisf(0, 0.0);
test__floatundisf(1, 1.0);
test__floatundisf(2, 2.0);
test__floatundisf(0x7FFFFF8000000000, 0x1.FFFFFEp+62);
test__floatundisf(0x7FFFFF0000000000, 0x1.FFFFFCp+62);
test__floatundisf(0x8000008000000000, 0x1p+63);
test__floatundisf(0x8000010000000000, 0x1.000002p+63);
test__floatundisf(0x8000000000000000, 0x1p+63);
test__floatundisf(0x8000000000000001, 0x1p+63);
test__floatundisf(0xFFFFFFFFFFFFFFFE, 0x1p+64);
test__floatundisf(0xFFFFFFFFFFFFFFFF, 0x1p+64);
test__floatundisf(0x0007FB72E8000000, 0x1.FEDCBAp+50);
test__floatundisf(0x0007FB72EA000000, 0x1.FEDCBAp+50);
test__floatundisf(0x0007FB72EB000000, 0x1.FEDCBAp+50);
test__floatundisf(0x0007FB72EBFFFFFF, 0x1.FEDCBAp+50);
test__floatundisf(0x0007FB72EC000000, 0x1.FEDCBCp+50);
test__floatundisf(0x0007FB72E8000001, 0x1.FEDCBAp+50);
test__floatundisf(0x0007FB72E6000000, 0x1.FEDCBAp+50);
test__floatundisf(0x0007FB72E7000000, 0x1.FEDCBAp+50);
test__floatundisf(0x0007FB72E7FFFFFF, 0x1.FEDCBAp+50);
test__floatundisf(0x0007FB72E4000001, 0x1.FEDCBAp+50);
test__floatundisf(0x0007FB72E4000000, 0x1.FEDCB8p+50);
}
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