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torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/arch/mips/math-emu/dp_tlong.c
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// SPDX-License-Identifier: GPL-2.0-only

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/* IEEE754 floating point arithmetic

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 * double precision: common utilities

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 */

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/*

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 * MIPS floating point support

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 * Copyright (C) 1994-2000 Algorithmics Ltd.

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 */

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#include "ieee754dp.h"

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s64 ieee754dp_tlong(union ieee754dp x)

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{

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	u64 residue;

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	int round;

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	int sticky;

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	int odd;

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	COMPXDP;

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	ieee754_clearcx();

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	EXPLODEXDP;

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	FLUSHXDP;

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	switch (xc) {

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	case IEEE754_CLASS_SNAN:

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	case IEEE754_CLASS_QNAN:

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		ieee754_setcx(IEEE754_INVALID_OPERATION);

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		return ieee754di_indef();

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	case IEEE754_CLASS_INF:

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		ieee754_setcx(IEEE754_INVALID_OPERATION);

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		return ieee754di_overflow(xs);

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	case IEEE754_CLASS_ZERO:

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		return 0;

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	case IEEE754_CLASS_DNORM:

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	case IEEE754_CLASS_NORM:

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		break;

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	}

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	if (xe >= 63) {

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		/* look for valid corner case */

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		if (xe == 63 && xs && xm == DP_HIDDEN_BIT)

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			return -0x8000000000000000LL;

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		/* Set invalid. We will only use overflow for floating

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		   point overflow */

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		ieee754_setcx(IEEE754_INVALID_OPERATION);

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		return ieee754di_overflow(xs);

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	}

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	/* oh gawd */

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	if (xe > DP_FBITS) {

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		xm <<= xe - DP_FBITS;

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	} else if (xe < DP_FBITS) {

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		if (xe < -1) {

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			residue = xm;

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			round = 0;

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			sticky = residue != 0;

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			xm = 0;

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		} else {

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			/* Shifting a u64 64 times does not work,

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			* so we do it in two steps. Be aware that xe

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			* may be -1 */

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			residue = xm << (xe + 1);

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			residue <<= 63 - DP_FBITS;

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			round = (residue >> 63) != 0;

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			sticky = (residue << 1) != 0;

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			xm >>= DP_FBITS - xe;

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		}

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		odd = (xm & 0x1) != 0x0;

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		switch (ieee754_csr.rm) {

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		case FPU_CSR_RN:

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			if (round && (sticky || odd))

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				xm++;

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			break;

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		case FPU_CSR_RZ:

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			break;

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		case FPU_CSR_RU:	/* toward +Infinity */

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			if ((round || sticky) && !xs)

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				xm++;

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			break;

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		case FPU_CSR_RD:	/* toward -Infinity */

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			if ((round || sticky) && xs)

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				xm++;

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			break;

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		}

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		if ((xm >> 63) != 0) {

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			/* This can happen after rounding */

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			ieee754_setcx(IEEE754_INVALID_OPERATION);

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			return ieee754di_overflow(xs);

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		}

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		if (round || sticky)

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			ieee754_setcx(IEEE754_INEXACT);

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	}

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	if (xs)

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		return -xm;

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	else

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		return xm;

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}

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