56 lines
2.0 KiB
Zig
56 lines
2.0 KiB
Zig
const Int = @import("std").meta.Int;
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const math = @import("std").math;
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const Log2Int = math.Log2Int;
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pub inline fn intFromFloat(comptime I: type, a: anytype) I {
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const F = @TypeOf(a);
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const float_bits = @typeInfo(F).Float.bits;
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const int_bits = @typeInfo(I).Int.bits;
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const rep_t = Int(.unsigned, float_bits);
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const sig_bits = math.floatMantissaBits(F);
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const exp_bits = math.floatExponentBits(F);
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const fractional_bits = math.floatFractionalBits(F);
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const implicit_bit = if (F != f80) (@as(rep_t, 1) << sig_bits) else 0;
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const max_exp = (1 << (exp_bits - 1));
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const exp_bias = max_exp - 1;
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const sig_mask = (@as(rep_t, 1) << sig_bits) - 1;
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// Break a into sign, exponent, significand
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const a_rep: rep_t = @bitCast(a);
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const negative = (a_rep >> (float_bits - 1)) != 0;
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const exponent = @as(i32, @intCast((a_rep << 1) >> (sig_bits + 1))) - exp_bias;
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const significand: rep_t = (a_rep & sig_mask) | implicit_bit;
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// If the exponent is negative, the result rounds to zero.
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if (exponent < 0) return 0;
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// If the value is too large for the integer type, saturate.
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switch (@typeInfo(I).Int.signedness) {
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.unsigned => {
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if (negative) return 0;
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if (@as(c_uint, @intCast(exponent)) >= @min(int_bits, max_exp)) return math.maxInt(I);
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},
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.signed => if (@as(c_uint, @intCast(exponent)) >= @min(int_bits - 1, max_exp)) {
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return if (negative) math.minInt(I) else math.maxInt(I);
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},
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}
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// If 0 <= exponent < sig_bits, right shift to get the result.
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// Otherwise, shift left.
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var result: I = undefined;
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if (exponent < fractional_bits) {
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result = @intCast(significand >> @intCast(fractional_bits - exponent));
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} else {
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result = @as(I, @intCast(significand)) << @intCast(exponent - fractional_bits);
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}
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if ((@typeInfo(I).Int.signedness == .signed) and negative)
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return ~result +% 1;
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return result;
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}
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test {
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_ = @import("int_from_float_test.zig");
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}
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