Stephen Hines | 6a211c5 | 2014-07-21 00:49:56 -0700 | [diff] [blame] | 1 | //=-lib/fp_extend_impl.inc - low precision -> high precision conversion -*-- -// |
| 2 | // |
| 3 | // The LLVM Compiler Infrastructure |
| 4 | // |
| 5 | // This file is dual licensed under the MIT and the University of Illinois Open |
| 6 | // Source Licenses. See LICENSE.TXT for details. |
| 7 | // |
| 8 | //===----------------------------------------------------------------------===// |
| 9 | // |
| 10 | // This file implements a fairly generic conversion from a narrower to a wider |
| 11 | // IEEE-754 floating-point type. The constants and types defined following the |
| 12 | // includes below parameterize the conversion. |
| 13 | // |
| 14 | // It does not support types that don't use the usual IEEE-754 interchange |
| 15 | // formats; specifically, some work would be needed to adapt it to |
| 16 | // (for example) the Intel 80-bit format or PowerPC double-double format. |
| 17 | // |
| 18 | // Note please, however, that this implementation is only intended to support |
| 19 | // *widening* operations; if you need to convert to a *narrower* floating-point |
| 20 | // type (e.g. double -> float), then this routine will not do what you want it |
| 21 | // to. |
| 22 | // |
| 23 | // It also requires that integer types at least as large as both formats |
| 24 | // are available on the target platform; this may pose a problem when trying |
| 25 | // to add support for quad on some 32-bit systems, for example. You also may |
| 26 | // run into trouble finding an appropriate CLZ function for wide source types; |
| 27 | // you will likely need to roll your own on some platforms. |
| 28 | // |
| 29 | // Finally, the following assumptions are made: |
| 30 | // |
| 31 | // 1. floating-point types and integer types have the same endianness on the |
| 32 | // target platform |
| 33 | // |
| 34 | // 2. quiet NaNs, if supported, are indicated by the leading bit of the |
| 35 | // significand field being set |
| 36 | // |
| 37 | //===----------------------------------------------------------------------===// |
| 38 | |
| 39 | #include "fp_extend.h" |
| 40 | |
Pirama Arumuga Nainar | 799172d | 2016-03-03 15:50:30 -0800 | [diff] [blame^] | 41 | static __inline dst_t __extendXfYf2__(src_t a) { |
Stephen Hines | 6a211c5 | 2014-07-21 00:49:56 -0700 | [diff] [blame] | 42 | // Various constants whose values follow from the type parameters. |
| 43 | // Any reasonable optimizer will fold and propagate all of these. |
| 44 | const int srcBits = sizeof(src_t)*CHAR_BIT; |
| 45 | const int srcExpBits = srcBits - srcSigBits - 1; |
| 46 | const int srcInfExp = (1 << srcExpBits) - 1; |
| 47 | const int srcExpBias = srcInfExp >> 1; |
| 48 | |
| 49 | const src_rep_t srcMinNormal = SRC_REP_C(1) << srcSigBits; |
| 50 | const src_rep_t srcInfinity = (src_rep_t)srcInfExp << srcSigBits; |
| 51 | const src_rep_t srcSignMask = SRC_REP_C(1) << (srcSigBits + srcExpBits); |
| 52 | const src_rep_t srcAbsMask = srcSignMask - 1; |
| 53 | const src_rep_t srcQNaN = SRC_REP_C(1) << (srcSigBits - 1); |
| 54 | const src_rep_t srcNaNCode = srcQNaN - 1; |
| 55 | |
| 56 | const int dstBits = sizeof(dst_t)*CHAR_BIT; |
| 57 | const int dstExpBits = dstBits - dstSigBits - 1; |
| 58 | const int dstInfExp = (1 << dstExpBits) - 1; |
| 59 | const int dstExpBias = dstInfExp >> 1; |
| 60 | |
| 61 | const dst_rep_t dstMinNormal = DST_REP_C(1) << dstSigBits; |
| 62 | |
| 63 | // Break a into a sign and representation of the absolute value |
| 64 | const src_rep_t aRep = srcToRep(a); |
| 65 | const src_rep_t aAbs = aRep & srcAbsMask; |
| 66 | const src_rep_t sign = aRep & srcSignMask; |
| 67 | dst_rep_t absResult; |
| 68 | |
Pirama Arumuga Nainar | a4cf3ee | 2015-05-20 13:03:23 -0700 | [diff] [blame] | 69 | // If sizeof(src_rep_t) < sizeof(int), the subtraction result is promoted |
| 70 | // to (signed) int. To avoid that, explicitly cast to src_rep_t. |
| 71 | if ((src_rep_t)(aAbs - srcMinNormal) < srcInfinity - srcMinNormal) { |
Stephen Hines | 6a211c5 | 2014-07-21 00:49:56 -0700 | [diff] [blame] | 72 | // a is a normal number. |
| 73 | // Extend to the destination type by shifting the significand and |
| 74 | // exponent into the proper position and rebiasing the exponent. |
| 75 | absResult = (dst_rep_t)aAbs << (dstSigBits - srcSigBits); |
| 76 | absResult += (dst_rep_t)(dstExpBias - srcExpBias) << dstSigBits; |
| 77 | } |
| 78 | |
| 79 | else if (aAbs >= srcInfinity) { |
| 80 | // a is NaN or infinity. |
| 81 | // Conjure the result by beginning with infinity, then setting the qNaN |
| 82 | // bit (if needed) and right-aligning the rest of the trailing NaN |
| 83 | // payload field. |
| 84 | absResult = (dst_rep_t)dstInfExp << dstSigBits; |
| 85 | absResult |= (dst_rep_t)(aAbs & srcQNaN) << (dstSigBits - srcSigBits); |
| 86 | absResult |= (dst_rep_t)(aAbs & srcNaNCode) << (dstSigBits - srcSigBits); |
| 87 | } |
| 88 | |
| 89 | else if (aAbs) { |
| 90 | // a is denormal. |
| 91 | // renormalize the significand and clear the leading bit, then insert |
| 92 | // the correct adjusted exponent in the destination type. |
| 93 | const int scale = src_rep_t_clz(aAbs) - src_rep_t_clz(srcMinNormal); |
| 94 | absResult = (dst_rep_t)aAbs << (dstSigBits - srcSigBits + scale); |
| 95 | absResult ^= dstMinNormal; |
| 96 | const int resultExponent = dstExpBias - srcExpBias - scale + 1; |
| 97 | absResult |= (dst_rep_t)resultExponent << dstSigBits; |
| 98 | } |
| 99 | |
| 100 | else { |
| 101 | // a is zero. |
| 102 | absResult = 0; |
| 103 | } |
| 104 | |
| 105 | // Apply the signbit to (dst_t)abs(a). |
| 106 | const dst_rep_t result = absResult | (dst_rep_t)sign << (dstBits - srcBits); |
| 107 | return dstFromRep(result); |
| 108 | } |