51 lines
1.9 KiB
Zig
51 lines
1.9 KiB
Zig
const std = @import("std");
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const common = @import("./common.zig");
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pub const panic = common.panic;
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comptime {
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@export(__extendxftf2, .{ .name = "__extendxftf2", .linkage = common.linkage });
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}
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fn __extendxftf2(a: f80) callconv(.C) f128 {
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const src_int_bit: u64 = 0x8000000000000000;
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const src_sig_mask = ~src_int_bit;
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const src_sig_bits = std.math.floatMantissaBits(f80) - 1; // -1 for the integer bit
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const dst_sig_bits = std.math.floatMantissaBits(f128);
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const dst_bits = @bitSizeOf(f128);
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const dst_min_normal = @as(u128, 1) << dst_sig_bits;
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// Break a into a sign and representation of the absolute value
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var a_rep = std.math.break_f80(a);
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const sign = a_rep.exp & 0x8000;
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a_rep.exp &= 0x7FFF;
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var abs_result: u128 = undefined;
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if (a_rep.exp == 0 and a_rep.fraction == 0) {
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// zero
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abs_result = 0;
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} else if (a_rep.exp == 0x7FFF) {
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// a is nan or infinite
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abs_result = @as(u128, a_rep.fraction) << (dst_sig_bits - src_sig_bits);
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abs_result |= @as(u128, a_rep.exp) << dst_sig_bits;
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} else if (a_rep.fraction & src_int_bit != 0) {
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// a is a normal value
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abs_result = @as(u128, a_rep.fraction & src_sig_mask) << (dst_sig_bits - src_sig_bits);
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abs_result |= @as(u128, a_rep.exp) << dst_sig_bits;
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} else {
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// a is denormal
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// renormalize the significand and clear the leading bit and integer part,
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// then insert the correct adjusted exponent in the destination type.
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const scale: u32 = @clz(a_rep.fraction);
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abs_result = @as(u128, a_rep.fraction) << @intCast(u7, dst_sig_bits - src_sig_bits + scale + 1);
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abs_result ^= dst_min_normal;
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abs_result |= @as(u128, scale + 1) << dst_sig_bits;
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}
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// Apply the signbit to (dst_t)abs(a).
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const result: u128 align(@alignOf(f128)) = abs_result | @as(u128, sign) << (dst_bits - 16);
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return @bitCast(f128, result);
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}
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