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d29871977f
We already have a LICENSE file that covers the Zig Standard Library. We no longer need to remind everyone that the license is MIT in every single file. Previously this was introduced to clarify the situation for a fork of Zig that made Zig's LICENSE file harder to find, and replaced it with their own license that required annual payments to their company. However that fork now appears to be dead. So there is no need to reinforce the copyright notice in every single file.
63 lines
2.2 KiB
Zig
63 lines
2.2 KiB
Zig
const builtin = @import("builtin");
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const is_test = builtin.is_test;
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const std = @import("std");
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const maxInt = std.math.maxInt;
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const LDBL_MANT_DIG = 113;
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pub fn __floatuntitf(arg: u128) callconv(.C) f128 {
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@setRuntimeSafety(is_test);
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if (arg == 0)
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return 0.0;
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var a = arg;
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const N: u32 = @sizeOf(u128) * 8;
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const sd = @bitCast(i32, N - @clz(u128, a)); // number of significant digits
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var e: i32 = sd - 1; // exponent
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if (sd > LDBL_MANT_DIG) {
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// start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
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// finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
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// 12345678901234567890123456
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// 1 = msb 1 bit
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// P = bit LDBL_MANT_DIG-1 bits to the right of 1
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// Q = bit LDBL_MANT_DIG bits to the right of 1
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// R = "or" of all bits to the right of Q
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switch (sd) {
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LDBL_MANT_DIG + 1 => {
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a <<= 1;
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},
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LDBL_MANT_DIG + 2 => {},
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else => {
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const shift_amt = @bitCast(i32, N + (LDBL_MANT_DIG + 2)) - sd;
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const shift_amt_u7 = @intCast(u7, shift_amt);
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a = (a >> @intCast(u7, sd - (LDBL_MANT_DIG + 2))) |
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@boolToInt((a & (@as(u128, maxInt(u128)) >> shift_amt_u7)) != 0);
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},
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}
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// finish
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a |= @boolToInt((a & 4) != 0); // Or P into R
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a += 1; // round - this step may add a significant bit
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a >>= 2; // dump Q and R
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// a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits
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if ((a & (@as(u128, 1) << LDBL_MANT_DIG)) != 0) {
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a >>= 1;
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e += 1;
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}
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// a is now rounded to LDBL_MANT_DIG bits
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} else {
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a <<= @intCast(u7, LDBL_MANT_DIG - sd);
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// a is now rounded to LDBL_MANT_DIG bits
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}
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const high: u128 = (@intCast(u64, (e + 16383)) << 48) | // exponent
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(@truncate(u64, a >> 64) & 0x0000ffffffffffff); // mantissa-high
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const low = @truncate(u64, a); // mantissa-low
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return @bitCast(f128, low | (high << 64));
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}
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test "import floatuntitf" {
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_ = @import("floatuntitf_test.zig");
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}
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