34 lines
1.0 KiB
Zig
34 lines
1.0 KiB
Zig
const builtin = @import("builtin");
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const std = @import("std");
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const maxInt = std.math.maxInt;
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const implicitBit = u64(1) << 52;
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pub extern fn __floatunsidf(arg: u32) f64 {
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@setRuntimeSafety(builtin.is_test);
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if (arg == 0) return 0.0;
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// The exponent is the width of abs(a)
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const exp = u64(31) - @clz(u32, arg);
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// Shift a into the significand field and clear the implicit bit
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const shift = @intCast(u6, 52 - exp);
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const mant = u64(arg) << shift ^ implicitBit;
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return @bitCast(f64, mant | (exp + 1023) << 52);
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}
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fn test_one_floatunsidf(a: u32, expected: u64) void {
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const r = __floatunsidf(a);
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std.testing.expect(@bitCast(u64, r) == expected);
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}
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test "floatsidf" {
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// Test the produced bit pattern
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test_one_floatunsidf(0, 0x0000000000000000);
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test_one_floatunsidf(1, 0x3ff0000000000000);
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test_one_floatunsidf(0x7FFFFFFF, 0x41dfffffffc00000);
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test_one_floatunsidf(@intCast(u32, 0x80000000), 0x41e0000000000000);
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test_one_floatunsidf(@intCast(u32, 0xFFFFFFFF), 0x41efffffffe00000);
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}
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