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add casting docs, __extenddftf2, and __extendsftf2
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,87 @@ | ||
| const std = @import("std"); | ||
| const builtin = @import("builtin"); | ||
| const is_test = builtin.is_test; | ||
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| pub extern fn __extenddftf2(a: f64) f128 { | ||
| return extendXfYf2(f128, f64, a); | ||
| } | ||
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| pub extern fn __extendsftf2(a: f32) f128 { | ||
| return extendXfYf2(f128, f32, a); | ||
| } | ||
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| const CHAR_BIT = 8; | ||
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| pub fn extendXfYf2(comptime dst_t: type, comptime src_t: type, a: src_t) dst_t { | ||
| const src_rep_t = @IntType(false, @typeInfo(src_t).Float.bits); | ||
| const dst_rep_t = @IntType(false, @typeInfo(dst_t).Float.bits); | ||
| const srcSigBits = std.math.floatMantissaBits(src_t); | ||
| const dstSigBits = std.math.floatMantissaBits(dst_t); | ||
| const SrcShift = std.math.Log2Int(src_rep_t); | ||
| const DstShift = std.math.Log2Int(dst_rep_t); | ||
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| // Various constants whose values follow from the type parameters. | ||
| // Any reasonable optimizer will fold and propagate all of these. | ||
| const srcBits: i32 = @sizeOf(src_t) * CHAR_BIT; | ||
| const srcExpBits: i32 = srcBits - srcSigBits - 1; | ||
| const srcInfExp: i32 = (1 << srcExpBits) - 1; | ||
| const srcExpBias: i32 = srcInfExp >> 1; | ||
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| const srcMinNormal: src_rep_t = src_rep_t(1) << srcSigBits; | ||
| const srcInfinity: src_rep_t = src_rep_t(@bitCast(u32, srcInfExp)) << srcSigBits; | ||
| const srcSignMask: src_rep_t = src_rep_t(1) << @intCast(SrcShift, srcSigBits +% srcExpBits); | ||
| const srcAbsMask: src_rep_t = srcSignMask -% 1; | ||
| const srcQNaN: src_rep_t = src_rep_t(1) << @intCast(SrcShift, srcSigBits -% 1); | ||
| const srcNaNCode: src_rep_t = srcQNaN -% 1; | ||
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| const dstBits: i32 = @sizeOf(dst_t) * CHAR_BIT; | ||
| const dstExpBits: i32 = dstBits - dstSigBits - 1; | ||
| const dstInfExp: i32 = (1 << dstExpBits) - 1; | ||
| const dstExpBias: i32 = dstInfExp >> 1; | ||
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| const dstMinNormal: dst_rep_t = dst_rep_t(1) << dstSigBits; | ||
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| // Break a into a sign and representation of the absolute value | ||
| const aRep: src_rep_t = @bitCast(src_rep_t, a); | ||
| const aAbs: src_rep_t = aRep & srcAbsMask; | ||
| const sign: src_rep_t = aRep & srcSignMask; | ||
| var absResult: dst_rep_t = undefined; | ||
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| // If @sizeOf(src_rep_t) < @sizeOf(int), the subtraction result is promoted | ||
| // to (signed) int. To avoid that, explicitly cast to src_rep_t. | ||
| if ((src_rep_t)(aAbs -% srcMinNormal) < srcInfinity -% srcMinNormal) { | ||
| // a is a normal number. | ||
| // Extend to the destination type by shifting the significand and | ||
| // exponent into the proper position and rebiasing the exponent. | ||
| absResult = dst_rep_t(aAbs) << (dstSigBits -% srcSigBits); | ||
| absResult += dst_rep_t(@bitCast(u32, dstExpBias -% srcExpBias)) << dstSigBits; | ||
| } else if (aAbs >= srcInfinity) { | ||
| // a is NaN or infinity. | ||
| // Conjure the result by beginning with infinity, then setting the qNaN | ||
| // bit (if needed) and right-aligning the rest of the trailing NaN | ||
| // payload field. | ||
| absResult = dst_rep_t(@bitCast(u32, dstInfExp)) << dstSigBits; | ||
| absResult |= (dst_rep_t)(aAbs & srcQNaN) << (dstSigBits - srcSigBits); | ||
| absResult |= (dst_rep_t)(aAbs & srcNaNCode) << (dstSigBits - srcSigBits); | ||
| } else if (aAbs != 0) { | ||
| // a is denormal. | ||
| // renormalize the significand and clear the leading bit, then insert | ||
| // the correct adjusted exponent in the destination type. | ||
| const scale: i32 = @clz(aAbs) - @clz(srcMinNormal); | ||
| absResult = dst_rep_t(aAbs) << @intCast(DstShift, dstSigBits - srcSigBits + scale); | ||
| absResult ^= dstMinNormal; | ||
| const resultExponent: i32 = dstExpBias - srcExpBias - scale + 1; | ||
| absResult |= dst_rep_t(@bitCast(u32, resultExponent)) << @intCast(DstShift, dstSigBits); | ||
| } else { | ||
| // a is zero. | ||
| absResult = 0; | ||
| } | ||
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| // Apply the signbit to (dst_t)abs(a). | ||
| const result: dst_rep_t align(@alignOf(dst_t)) = absResult | dst_rep_t(sign) << @intCast(DstShift, dstBits - srcBits); | ||
| return @bitCast(dst_t, result); | ||
| } | ||
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| test "import extendXfYf2" { | ||
| _ = @import("extendXfYf2_test.zig"); | ||
| } |
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