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torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/arch/x86/math-emu/reg_mul.c
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// SPDX-License-Identifier: GPL-2.0

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/*---------------------------------------------------------------------------+

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 |  reg_mul.c                                                                |

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 |                                                                           |

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 | Multiply one FPU_REG by another, put the result in a destination FPU_REG. |

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 |                                                                           |

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 | Copyright (C) 1992,1993,1997                                              |

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 |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |

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 |                  E-mail   [email protected]                              |

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 |                                                                           |

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 | Returns the tag of the result if no exceptions or errors occurred.        |

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 |                                                                           |

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 +---------------------------------------------------------------------------*/

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/*---------------------------------------------------------------------------+

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 | The destination may be any FPU_REG, including one of the source FPU_REGs. |

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 +---------------------------------------------------------------------------*/

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#include "fpu_emu.h"

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#include "exception.h"

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#include "reg_constant.h"

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#include "fpu_system.h"

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/*

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  Multiply two registers to give a register result.

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  The sources are st(deststnr) and (b,tagb,signb).

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  The destination is st(deststnr).

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  */

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/* This routine must be called with non-empty source registers */

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int FPU_mul(FPU_REG const *b, u_char tagb, int deststnr, int control_w)

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{

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	FPU_REG *a = &st(deststnr);

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	FPU_REG *dest = a;

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	u_char taga = FPU_gettagi(deststnr);

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	u_char saved_sign = getsign(dest);

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	u_char sign = (getsign(a) ^ getsign(b));

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	int tag;

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	if (!(taga | tagb)) {

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		/* Both regs Valid, this should be the most common case. */

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		tag =

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		    FPU_u_mul(a, b, dest, control_w, sign,

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			      exponent(a) + exponent(b));

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		if (tag < 0) {

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			setsign(dest, saved_sign);

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			return tag;

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		}

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		FPU_settagi(deststnr, tag);

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		return tag;

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	}

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	if (taga == TAG_Special)

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		taga = FPU_Special(a);

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	if (tagb == TAG_Special)

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		tagb = FPU_Special(b);

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	if (((taga == TAG_Valid) && (tagb == TW_Denormal))

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	    || ((taga == TW_Denormal) && (tagb == TAG_Valid))

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	    || ((taga == TW_Denormal) && (tagb == TW_Denormal))) {

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		FPU_REG x, y;

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		if (denormal_operand() < 0)

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			return FPU_Exception;

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		FPU_to_exp16(a, &x);

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		FPU_to_exp16(b, &y);

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		tag = FPU_u_mul(&x, &y, dest, control_w, sign,

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				exponent16(&x) + exponent16(&y));

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		if (tag < 0) {

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			setsign(dest, saved_sign);

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			return tag;

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		}

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		FPU_settagi(deststnr, tag);

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		return tag;

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	} else if ((taga <= TW_Denormal) && (tagb <= TW_Denormal)) {

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		if (((tagb == TW_Denormal) || (taga == TW_Denormal))

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		    && (denormal_operand() < 0))

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			return FPU_Exception;

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		/* Must have either both arguments == zero, or

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		   one valid and the other zero.

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		   The result is therefore zero. */

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		FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);

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		/* The 80486 book says that the answer is +0, but a real

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		   80486 behaves this way.

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		   IEEE-754 apparently says it should be this way. */

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		setsign(dest, sign);

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		return TAG_Zero;

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	}

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	/* Must have infinities, NaNs, etc */

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	else if ((taga == TW_NaN) || (tagb == TW_NaN)) {

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		return real_2op_NaN(b, tagb, deststnr, &st(0));

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	} else if (((taga == TW_Infinity) && (tagb == TAG_Zero))

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		   || ((tagb == TW_Infinity) && (taga == TAG_Zero))) {

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		return arith_invalid(deststnr);	/* Zero*Infinity is invalid */

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	} else if (((taga == TW_Denormal) || (tagb == TW_Denormal))

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		   && (denormal_operand() < 0)) {

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		return FPU_Exception;

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	} else if (taga == TW_Infinity) {

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		FPU_copy_to_regi(a, TAG_Special, deststnr);

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		setsign(dest, sign);

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		return TAG_Special;

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	} else if (tagb == TW_Infinity) {

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		FPU_copy_to_regi(b, TAG_Special, deststnr);

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		setsign(dest, sign);

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		return TAG_Special;

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	}

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#ifdef PARANOID

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	else {

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		EXCEPTION(EX_INTERNAL | 0x102);

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		return FPU_Exception;

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	}

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#endif /* PARANOID */

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	return 0;

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}

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