52 lines
1.9 KiB
Zig
52 lines
1.9 KiB
Zig
const is_test = @import("builtin").is_test;
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const Log2Int = @import("std").math.Log2Int;
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pub fn fixuint(comptime fp_t: type, comptime fixuint_t: type, a: fp_t) fixuint_t {
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@setRuntimeSafety(is_test);
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const rep_t = switch (fp_t) {
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f32 => u32,
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f64 => u64,
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f128 => u128,
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else => unreachable,
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};
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const srep_t = @import("std").meta.IntType(true, rep_t.bit_count);
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const significandBits = switch (fp_t) {
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f32 => 23,
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f64 => 52,
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f128 => 112,
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else => unreachable,
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};
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const typeWidth = rep_t.bit_count;
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const exponentBits = (typeWidth - significandBits - 1);
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const signBit = (@as(rep_t, 1) << (significandBits + exponentBits));
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const maxExponent = ((1 << exponentBits) - 1);
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const exponentBias = (maxExponent >> 1);
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const implicitBit = (@as(rep_t, 1) << significandBits);
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const significandMask = (implicitBit - 1);
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// Break a into sign, exponent, significand
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const aRep: rep_t = @bitCast(rep_t, a);
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const absMask = signBit - 1;
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const aAbs: rep_t = aRep & absMask;
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const sign = if ((aRep & signBit) != 0) @as(i32, -1) else @as(i32, 1);
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const exponent = @intCast(i32, aAbs >> significandBits) - exponentBias;
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const significand: rep_t = (aAbs & significandMask) | implicitBit;
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// If either the value or the exponent is negative, the result is zero.
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if (sign == -1 or exponent < 0) return 0;
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// If the value is too large for the integer type, saturate.
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if (@intCast(c_uint, exponent) >= fixuint_t.bit_count) return ~@as(fixuint_t, 0);
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// If 0 <= exponent < significandBits, right shift to get the result.
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// Otherwise, shift left.
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if (exponent < significandBits) {
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return @intCast(fixuint_t, significand >> @intCast(Log2Int(rep_t), significandBits - exponent));
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} else {
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return @intCast(fixuint_t, significand) << @intCast(Log2Int(fixuint_t), exponent - significandBits);
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}
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}
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