60 lines
2.2 KiB
Zig
60 lines
2.2 KiB
Zig
const is_test = @import("builtin").is_test;
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const Log2Int = @import("../../math/index.zig").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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@setDebugSafety(this, 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 = @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 = (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 = (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) i32(-1) else i32(1);
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const exponent = 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)
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return 0;
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// If the value is too large for the integer type, saturate.
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if (c_uint(exponent) >= fixuint_t.bit_count)
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return ~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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// TODO this is a workaround for the mysterious "integer cast truncated bits"
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// happening on the next line
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@setDebugSafety(this, false);
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return fixuint_t(significand >> Log2Int(rep_t)(significandBits - exponent));
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} else {
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// TODO this is a workaround for the mysterious "integer cast truncated bits"
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// happening on the next line
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@setDebugSafety(this, false);
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return fixuint_t(significand) << Log2Int(fixuint_t)(exponent - significandBits);
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}
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}
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