//= lib/fp_trunc_impl.inc - high precision -> low precision conversion *-*-===//

//

//                     The LLVM Compiler Infrastructure

//

// This file is dual licensed under the MIT and the University of Illinois Open

// Source Licenses. See LICENSE.TXT for details.

//

//===----------------------------------------------------------------------===//

//

// This file implements a fairly generic conversion from a wider to a narrower

// IEEE-754 floating-point type in the default (round to nearest, ties to even)

// rounding mode.  The constants and types defined following the includes below

// parameterize the conversion.

//

// This routine can be trivially adapted to support conversions to

// half-precision or from quad-precision. It does not support types that don't

// use the usual IEEE-754 interchange formats; specifically, some work would be

// needed to adapt it to (for example) the Intel 80-bit format or PowerPC

// double-double format.

//

// Note please, however, that this implementation is only intended to support

// *narrowing* operations; if you need to convert to a *wider* floating-point

// type (e.g. float -> double), then this routine will not do what you want it

// to.

//

// It also requires that integer types at least as large as both formats

// are available on the target platform; this may pose a problem when trying

// to add support for quad on some 32-bit systems, for example.

//

// Finally, the following assumptions are made:

//

// 1. floating-point types and integer types have the same endianness on the

//    target platform

//

// 2. quiet NaNs, if supported, are indicated by the leading bit of the

//    significand field being set

//

//===----------------------------------------------------------------------===//

#include "fp_trunc.h"

static __inline dst_t __truncXfYf2__(src_t a) {

    // Various constants whose values follow from the type parameters.

    // Any reasonable optimizer will fold and propagate all of these.

    const int srcBits = sizeof(src_t)*CHAR_BIT;

    const int srcExpBits = srcBits - srcSigBits - 1;

    const int srcInfExp = (1 << srcExpBits) - 1;

    const int srcExpBias = srcInfExp >> 1;

    const src_rep_t srcMinNormal = SRC_REP_C(1) << srcSigBits;

    const src_rep_t srcSignificandMask = srcMinNormal - 1;

    const src_rep_t srcInfinity = (src_rep_t)srcInfExp << srcSigBits;

    const src_rep_t srcSignMask = SRC_REP_C(1) << (srcSigBits + srcExpBits);

    const src_rep_t srcAbsMask = srcSignMask - 1;

    const src_rep_t roundMask = (SRC_REP_C(1) << (srcSigBits - dstSigBits)) - 1;

    const src_rep_t halfway = SRC_REP_C(1) << (srcSigBits - dstSigBits - 1);

    const src_rep_t srcQNaN = SRC_REP_C(1) << (srcSigBits - 1);

    const src_rep_t srcNaNCode = srcQNaN - 1;

    const int dstBits = sizeof(dst_t)*CHAR_BIT;

    const int dstExpBits = dstBits - dstSigBits - 1;

    const int dstInfExp = (1 << dstExpBits) - 1;

    const int dstExpBias = dstInfExp >> 1;

    const int underflowExponent = srcExpBias + 1 - dstExpBias;

    const int overflowExponent = srcExpBias + dstInfExp - dstExpBias;

    const src_rep_t underflow = (src_rep_t)underflowExponent << srcSigBits;

    const src_rep_t overflow = (src_rep_t)overflowExponent << srcSigBits;

    const dst_rep_t dstQNaN = DST_REP_C(1) << (dstSigBits - 1);

    const dst_rep_t dstNaNCode = dstQNaN - 1;

    // Break a into a sign and representation of the absolute value

    dst_rep_t absResult;

        // The exponent of a is within the range of normal numbers in the

        // destination format.  We can convert by simply right-shifting with

        // rounding and adjusting the exponent.

        // Round to nearest

        // Ties to even

    }

        // a is NaN.

        // Conjure the result by beginning with infinity, setting the qNaN

        // bit and inserting the (truncated) trailing NaN field.

        absResult = (dst_rep_t)dstInfExp << dstSigBits;

        absResult |= dstQNaN;

    }

        // a overflows to infinity.

        absResult = (dst_rep_t)dstInfExp << dstSigBits;

    }

    else {

        // a underflows on conversion to the destination type or is an exact

        // zero.  The result may be a denormal or zero.  Extract the exponent

        // to get the shift amount for the denormalization.

        // Right shift by the denormalization amount with sticky.

            absResult = 0;

            // Round to nearest

            // Ties to even

        }

    }

    // Apply the signbit to (dst_t)abs(a).

}