2004-01-06 Jeff Johnston <[email protected]>

[binutils.git] / gdb / i387-tdep.c

/* Intel 387 floating point stuff.

   Copyright 1988, 1989, 1991, 1992, 1993, 1994, 1998, 1999, 2000,
   2001, 2002, 2003 Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include "defs.h"
#include "doublest.h"
#include "floatformat.h"
#include "frame.h"
#include "gdbcore.h"
#include "inferior.h"
#include "language.h"
#include "regcache.h"
#include "value.h"

#include "gdb_assert.h"
#include "gdb_string.h"

#include "i386-tdep.h"
#include "i387-tdep.h"

/* Implement the `info float' layout based on the register definitions
   in `tm-i386.h'.  */

/* Print the floating point number specified by RAW.  */

static void
print_i387_value (char *raw, struct ui_file *file)
{
  DOUBLEST value;

  /* Using extract_typed_floating here might affect the representation
     of certain numbers such as NaNs, even if GDB is running natively.
     This is fine since our caller already detects such special
     numbers and we print the hexadecimal representation anyway.  */
  value = extract_typed_floating (raw, builtin_type_i387_ext);

  /* We try to print 19 digits.  The last digit may or may not contain
     garbage, but we'd better print one too many.  We need enough room
     to print the value, 1 position for the sign, 1 for the decimal
     point, 19 for the digits and 6 for the exponent adds up to 27.  */
#ifdef PRINTF_HAS_LONG_DOUBLE
  fprintf_filtered (file, " %-+27.19Lg", (long double) value);
#else
  fprintf_filtered (file, " %-+27.19g", (double) value);
#endif
}

/* Print the classification for the register contents RAW.  */

static void
print_i387_ext (unsigned char *raw, struct ui_file *file)
{
  int sign;
  int integer;
  unsigned int exponent;
  unsigned long fraction[2];

  sign = raw[9] & 0x80;
  integer = raw[7] & 0x80;
  exponent = (((raw[9] & 0x7f) << 8) | raw[8]);
  fraction[0] = ((raw[3] << 24) | (raw[2] << 16) | (raw[1] << 8) | raw[0]);
  fraction[1] = (((raw[7] & 0x7f) << 24) | (raw[6] << 16)
		 | (raw[5] << 8) | raw[4]);

  if (exponent == 0x7fff && integer)
    {
      if (fraction[0] == 0x00000000 && fraction[1] == 0x00000000)
	/* Infinity.  */
	fprintf_filtered (file, " %cInf", (sign ? '-' : '+'));
      else if (sign && fraction[0] == 0x00000000 && fraction[1] == 0x40000000)
	/* Real Indefinite (QNaN).  */
	fputs_unfiltered (" Real Indefinite (QNaN)", file);
      else if (fraction[1] & 0x40000000)
	/* QNaN.  */
	fputs_filtered (" QNaN", file);
      else
	/* SNaN.  */
	fputs_filtered (" SNaN", file);
    }
  else if (exponent < 0x7fff && exponent > 0x0000 && integer)
    /* Normal.  */
    print_i387_value (raw, file);
  else if (exponent == 0x0000)
    {
      /* Denormal or zero.  */
      print_i387_value (raw, file);
      
      if (integer)
	/* Pseudo-denormal.  */
	fputs_filtered (" Pseudo-denormal", file);
      else if (fraction[0] || fraction[1])
	/* Denormal.  */
	fputs_filtered (" Denormal", file);
    }
  else
    /* Unsupported.  */
    fputs_filtered (" Unsupported", file);
}

/* Print the status word STATUS.  */

static void
print_i387_status_word (unsigned int status, struct ui_file *file)
{
  fprintf_filtered (file, "Status Word:         %s",
		   local_hex_string_custom (status, "04"));
  fputs_filtered ("  ", file);
  fprintf_filtered (file, " %s", (status & 0x0001) ? "IE" : "  ");
  fprintf_filtered (file, " %s", (status & 0x0002) ? "DE" : "  ");
  fprintf_filtered (file, " %s", (status & 0x0004) ? "ZE" : "  ");
  fprintf_filtered (file, " %s", (status & 0x0008) ? "OE" : "  ");
  fprintf_filtered (file, " %s", (status & 0x0010) ? "UE" : "  ");
  fprintf_filtered (file, " %s", (status & 0x0020) ? "PE" : "  ");
  fputs_filtered ("  ", file);
  fprintf_filtered (file, " %s", (status & 0x0080) ? "ES" : "  ");
  fputs_filtered ("  ", file);
  fprintf_filtered (file, " %s", (status & 0x0040) ? "SF" : "  ");
  fputs_filtered ("  ", file);
  fprintf_filtered (file, " %s", (status & 0x0100) ? "C0" : "  ");
  fprintf_filtered (file, " %s", (status & 0x0200) ? "C1" : "  ");
  fprintf_filtered (file, " %s", (status & 0x0400) ? "C2" : "  ");
  fprintf_filtered (file, " %s", (status & 0x4000) ? "C3" : "  ");

  fputs_filtered ("\n", file);

  fprintf_filtered (file,
		    "                       TOP: %d\n", ((status >> 11) & 7));
}

/* Print the control word CONTROL.  */

static void
print_i387_control_word (unsigned int control, struct ui_file *file)
{
  fprintf_filtered (file, "Control Word:        %s",
		   local_hex_string_custom (control, "04"));
  fputs_filtered ("  ", file);
  fprintf_filtered (file, " %s", (control & 0x0001) ? "IM" : "  ");
  fprintf_filtered (file, " %s", (control & 0x0002) ? "DM" : "  ");
  fprintf_filtered (file, " %s", (control & 0x0004) ? "ZM" : "  ");
  fprintf_filtered (file, " %s", (control & 0x0008) ? "OM" : "  ");
  fprintf_filtered (file, " %s", (control & 0x0010) ? "UM" : "  ");
  fprintf_filtered (file, " %s", (control & 0x0020) ? "PM" : "  ");

  fputs_filtered ("\n", file);

  fputs_filtered ("                       PC: ", file);
  switch ((control >> 8) & 3)
    {
    case 0:
      fputs_filtered ("Single Precision (24-bits)\n", file);
      break;
    case 1:
      fputs_filtered ("Reserved\n", file);
      break;
    case 2:
      fputs_filtered ("Double Precision (53-bits)\n", file);
      break;
    case 3:
      fputs_filtered ("Extended Precision (64-bits)\n", file);
      break;
    }
      
  fputs_filtered ("                       RC: ", file);
  switch ((control >> 10) & 3)
    {
    case 0:
      fputs_filtered ("Round to nearest\n", file);
      break;
    case 1:
      fputs_filtered ("Round down\n", file);
      break;
    case 2:
      fputs_filtered ("Round up\n", file);
      break;
    case 3:
      fputs_filtered ("Round toward zero\n", file);
      break;
    }
}

/* Print out the i387 floating point state.  Note that we ignore FRAME
   in the code below.  That's OK since floating-point registers are
   never saved on the stack.  */

void
i387_print_float_info (struct gdbarch *gdbarch, struct ui_file *file,
		       struct frame_info *frame, const char *args)
{
  struct gdbarch_tdep *tdep = gdbarch_tdep (get_frame_arch (frame));
  char buf[4];
  ULONGEST fctrl;
  ULONGEST fstat;
  ULONGEST ftag;
  ULONGEST fiseg;
  ULONGEST fioff;
  ULONGEST foseg;
  ULONGEST fooff;
  ULONGEST fop;
  int fpreg;
  int top;

  gdb_assert (gdbarch == get_frame_arch (frame));

  /* Define I387_ST0_REGNUM such that we use the proper definitions
     for FRAME's architecture.  */
#define I387_ST0_REGNUM tdep->st0_regnum

  fctrl = get_frame_register_unsigned (frame, I387_FCTRL_REGNUM);
  fstat = get_frame_register_unsigned (frame, I387_FSTAT_REGNUM);
  ftag = get_frame_register_unsigned (frame, I387_FTAG_REGNUM);
  fiseg = get_frame_register_unsigned (frame, I387_FISEG_REGNUM);
  fioff = get_frame_register_unsigned (frame, I387_FIOFF_REGNUM);
  foseg = get_frame_register_unsigned (frame, I387_FOSEG_REGNUM);
  fooff = get_frame_register_unsigned (frame, I387_FOOFF_REGNUM);
  fop = get_frame_register_unsigned (frame, I387_FOP_REGNUM);

  top = ((fstat >> 11) & 7);

  for (fpreg = 7; fpreg >= 0; fpreg--)
    {
      unsigned char raw[I386_MAX_REGISTER_SIZE];
      int tag = (ftag >> (fpreg * 2)) & 3;
      int i;

      fprintf_filtered (file, "%sR%d: ", fpreg == top ? "=>" : "  ", fpreg);

      switch (tag)
	{
	case 0:
	  fputs_filtered ("Valid   ", file);
	  break;
	case 1:
	  fputs_filtered ("Zero    ", file);
	  break;
	case 2:
	  fputs_filtered ("Special ", file);
	  break;
	case 3:
	  fputs_filtered ("Empty   ", file);
	  break;
	}

      get_frame_register (frame, (fpreg + 8 - top) % 8 + I387_ST0_REGNUM, raw);

      fputs_filtered ("0x", file);
      for (i = 9; i >= 0; i--)
	fprintf_filtered (file, "%02x", raw[i]);

      if (tag != 3)
	print_i387_ext (raw, file);

      fputs_filtered ("\n", file);
    }

  fputs_filtered ("\n", file);

  print_i387_status_word (fstat, file);
  print_i387_control_word (fctrl, file);
  fprintf_filtered (file, "Tag Word:            %s\n",
		    local_hex_string_custom (ftag, "04"));
  fprintf_filtered (file, "Instruction Pointer: %s:",
		    local_hex_string_custom (fiseg, "02"));
  fprintf_filtered (file, "%s\n", local_hex_string_custom (fioff, "08"));
  fprintf_filtered (file, "Operand Pointer:     %s:",
		    local_hex_string_custom (foseg, "02"));
  fprintf_filtered (file, "%s\n", local_hex_string_custom (fooff, "08"));
  fprintf_filtered (file, "Opcode:              %s\n",
		    local_hex_string_custom (fop ? (fop | 0xd800) : 0, "04"));

#undef I387_ST0_REGNUM
}
\f

/* Read a value of type TYPE from register REGNUM in frame FRAME, and
   return its contents in TO.  */

void
i387_register_to_value (struct frame_info *frame, int regnum,
			struct type *type, void *to)
{
  char from[I386_MAX_REGISTER_SIZE];

  gdb_assert (i386_fp_regnum_p (regnum));

  /* We only support floating-point values.  */
  if (TYPE_CODE (type) != TYPE_CODE_FLT)
    {
      warning ("Cannot convert floating-point register value "
	       "to non-floating-point type.");
      return;
    }

  /* Convert to TYPE.  This should be a no-op if TYPE is equivalent to
     the extended floating-point format used by the FPU.  */
  get_frame_register (frame, regnum, from);
  convert_typed_floating (from, builtin_type_i387_ext, to, type);
}

/* Write the contents FROM of a value of type TYPE into register
   REGNUM in frame FRAME.  */

void
i387_value_to_register (struct frame_info *frame, int regnum,
			struct type *type, const void *from)
{
  char to[I386_MAX_REGISTER_SIZE];

  gdb_assert (i386_fp_regnum_p (regnum));

  /* We only support floating-point values.  */
  if (TYPE_CODE (type) != TYPE_CODE_FLT)
    {
      warning ("Cannot convert non-floating-point type "
	       "to floating-point register value.");
      return;
    }

  /* Convert from TYPE.  This should be a no-op if TYPE is equivalent
     to the extended floating-point format used by the FPU.  */
  convert_typed_floating (from, type, to, builtin_type_i387_ext);
  put_frame_register (frame, regnum, to);
}
\f
\f

/* Handle FSAVE and FXSAVE formats.  */

/* FIXME: kettenis/20030927: The functions below should accept a
   `regcache' argument, but I don't want to change the function
   signature just yet.  There's some band-aid in the functions below
   in the form of the `regcache' local variables.  This will ease the
   transition later on.  */

/* At fsave_offset[REGNUM] you'll find the offset to the location in
   the data structure used by the "fsave" instruction where GDB
   register REGNUM is stored.  */

static int fsave_offset[] =
{
  28 + 0 * 10,			/* %st(0) ...  */
  28 + 1 * 10,
  28 + 2 * 10,
  28 + 3 * 10,
  28 + 4 * 10,
  28 + 5 * 10,
  28 + 6 * 10,
  28 + 7 * 10,			/* ... %st(7).  */
  0,				/* `fctrl' (16 bits).  */
  4,				/* `fstat' (16 bits).  */
  8,				/* `ftag' (16 bits).  */
  16,				/* `fiseg' (16 bits).  */
  12,				/* `fioff'.  */
  24,				/* `foseg' (16 bits).  */
  20,				/* `fooff'.  */
  18				/* `fop' (bottom 11 bits).  */
};

#define FSAVE_ADDR(fsave, regnum) \
  (fsave + fsave_offset[regnum - I387_ST0_REGNUM])
\f

/* Fill register REGNUM in REGCACHE with the appropriate value from
   *FSAVE.  This function masks off any of the reserved bits in
   *FSAVE.  */

void
i387_supply_fsave (struct regcache *regcache, int regnum, const void *fsave)
{
  struct gdbarch_tdep *tdep = gdbarch_tdep (get_regcache_arch (regcache));
  const char *regs = fsave;
  int i;

  gdb_assert (tdep->st0_regnum >= I386_ST0_REGNUM);

  /* Define I387_ST0_REGNUM such that we use the proper definitions
     for REGCACHE's architecture.  */
#define I387_ST0_REGNUM tdep->st0_regnum

  for (i = I387_ST0_REGNUM; i < I387_XMM0_REGNUM; i++)
    if (regnum == -1 || regnum == i)
      {
	if (fsave == NULL)
	  {
	    regcache_raw_supply (regcache, i, NULL);
	    continue;
	  }

	/* Most of the FPU control registers occupy only 16 bits in the
	   fsave area.  Give those a special treatment.  */
	if (i >= I387_FCTRL_REGNUM
	    && i != I387_FIOFF_REGNUM && i != I387_FOOFF_REGNUM)
	  {
	    unsigned char val[4];

	    memcpy (val, FSAVE_ADDR (regs, i), 2);
	    val[2] = val[3] = 0;
	    if (i == I387_FOP_REGNUM)
	      val[1] &= ((1 << 3) - 1);
	    regcache_raw_supply (regcache, i, val);
	  }
	else
	  regcache_raw_supply (regcache, i, FSAVE_ADDR (regs, i));
      }
#undef I387_ST0_REGNUM
}

/* Fill register REGNUM (if it is a floating-point register) in *FSAVE
   with the value in GDB's register cache.  If REGNUM is -1, do this
   for all registers.  This function doesn't touch any of the reserved
   bits in *FSAVE.  */

void
i387_fill_fsave (void *fsave, int regnum)
{
  struct regcache *regcache = current_regcache;
  struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch);
  char *regs = fsave;
  int i;

  gdb_assert (tdep->st0_regnum >= I386_ST0_REGNUM);

  /* Define I387_ST0_REGNUM such that we use the proper definitions
     for REGCACHE's architecture.  */
#define I387_ST0_REGNUM tdep->st0_regnum

  for (i = I387_ST0_REGNUM; i < I387_XMM0_REGNUM; i++)
    if (regnum == -1 || regnum == i)
      {
	/* Most of the FPU control registers occupy only 16 bits in
           the fsave area.  Give those a special treatment.  */
	if (i >= I387_FCTRL_REGNUM
	    && i != I387_FIOFF_REGNUM && i != I387_FOOFF_REGNUM)
	  {
	    unsigned char buf[4];

	    regcache_raw_collect (regcache, i, buf);

	    if (i == I387_FOP_REGNUM)
	      {
		/* The opcode occupies only 11 bits.  Make sure we
                   don't touch the other bits.  */
		buf[1] &= ((1 << 3) - 1);
		buf[1] |= ((FSAVE_ADDR (regs, i))[1] & ~((1 << 3) - 1));
	      }
	    memcpy (FSAVE_ADDR (regs, i), buf, 2);
	  }
	else
	  regcache_raw_collect (regcache, i, FSAVE_ADDR (regs, i));
      }
#undef I387_ST0_REGNUM
}
\f

/* At fxsave_offset[REGNUM] you'll find the offset to the location in
   the data structure used by the "fxsave" instruction where GDB
   register REGNUM is stored.  */

static int fxsave_offset[] =
{
  32,				/* %st(0) through ...  */
  48,
  64,
  80,
  96,
  112,
  128,
  144,				/* ... %st(7) (80 bits each).  */
  0,				/* `fctrl' (16 bits).  */
  2,				/* `fstat' (16 bits).  */
  4,				/* `ftag' (16 bits).  */
  12,				/* `fiseg' (16 bits).  */
  8,				/* `fioff'.  */
  20,				/* `foseg' (16 bits).  */
  16,				/* `fooff'.  */
  6,				/* `fop' (bottom 11 bits).  */
  160 + 0 * 16,			/* %xmm0 through ...  */
  160 + 1 * 16,
  160 + 2 * 16,
  160 + 3 * 16,
  160 + 4 * 16,
  160 + 5 * 16,
  160 + 6 * 16,
  160 + 7 * 16,
  160 + 8 * 16,
  160 + 9 * 16,
  160 + 10 * 16,
  160 + 11 * 16,
  160 + 12 * 16,
  160 + 13 * 16,
  160 + 14 * 16,
  160 + 15 * 16,		/* ... %xmm15 (128 bits each).  */
};

#define FXSAVE_ADDR(fxsave, regnum) \
  (fxsave + fxsave_offset[regnum - I387_ST0_REGNUM])

/* We made an unfortunate choice in putting %mxcsr after the SSE
   registers %xmm0-%xmm7 instead of before, since it makes supporting
   the registers %xmm8-%xmm15 on AMD64 a bit involved.  Therefore we
   don't include the offset for %mxcsr here above.  */

#define FXSAVE_MXCSR_ADDR(fxsave) (fxsave + 24)

static int i387_tag (const unsigned char *raw);
\f

/* Fill register REGNUM in REGCACHE with the appropriate
   floating-point or SSE register value from *FXSAVE.  This function
   masks off any of the reserved bits in *FXSAVE.  */

void
i387_supply_fxsave (struct regcache *regcache, int regnum, const void *fxsave)
{
  struct gdbarch_tdep *tdep = gdbarch_tdep (get_regcache_arch (regcache));
  const char *regs = fxsave;
  int i;

  gdb_assert (tdep->st0_regnum >= I386_ST0_REGNUM);
  gdb_assert (tdep->num_xmm_regs > 0);

  /* Define I387_ST0_REGNUM and I387_NUM_XMM_REGS such that we use the
     proper definitions for REGCACHE's architecture.  */

#define I387_ST0_REGNUM	tdep->st0_regnum
#define I387_NUM_XMM_REGS tdep->num_xmm_regs

  for (i = I387_ST0_REGNUM; i < I387_MXCSR_REGNUM; i++)
    if (regnum == -1 || regnum == i)
      {
	if (regs == NULL)
	  {
	    regcache_raw_supply (regcache, i, NULL);
	    continue;
	  }

	/* Most of the FPU control registers occupy only 16 bits in
	   the fxsave area.  Give those a special treatment.  */
	if (i >= I387_FCTRL_REGNUM && i < I387_XMM0_REGNUM
	    && i != I387_FIOFF_REGNUM && i != I387_FOOFF_REGNUM)
	  {
	    unsigned char val[4];

	    memcpy (val, FXSAVE_ADDR (regs, i), 2);
	    val[2] = val[3] = 0;
	    if (i == I387_FOP_REGNUM)
	      val[1] &= ((1 << 3) - 1);
	    else if (i== I387_FTAG_REGNUM)
	      {
		/* The fxsave area contains a simplified version of
		   the tag word.  We have to look at the actual 80-bit
		   FP data to recreate the traditional i387 tag word.  */

		unsigned long ftag = 0;
		int fpreg;
		int top;

		top = ((FXSAVE_ADDR (regs, I387_FSTAT_REGNUM))[1] >> 3);
		top &= 0x7;

		for (fpreg = 7; fpreg >= 0; fpreg--)
		  {
		    int tag;

		    if (val[0] & (1 << fpreg))
		      {
			int regnum = (fpreg + 8 - top) % 8 + I387_ST0_REGNUM;
			tag = i387_tag (FXSAVE_ADDR (regs, regnum));
		      }
		    else
		      tag = 3;		/* Empty */

		    ftag |= tag << (2 * fpreg);
		  }
		val[0] = ftag & 0xff;
		val[1] = (ftag >> 8) & 0xff;
	      }
	    regcache_raw_supply (regcache, i, val);
	  }
	else
	  regcache_raw_supply (regcache, i, FXSAVE_ADDR (regs, i));
      }

  if (regnum == I387_MXCSR_REGNUM || regnum == -1)
    {
      if (regs == NULL)
	regcache_raw_supply (regcache, I387_MXCSR_REGNUM, NULL);
      else
	regcache_raw_supply (regcache, I387_MXCSR_REGNUM,
			     FXSAVE_MXCSR_ADDR (regs));
    }

#undef I387_ST0_REGNUM
#undef I387_NUM_XMM_REGS
}

/* Fill register REGNUM (if it is a floating-point or SSE register) in
   *FXSAVE with the value in GDB's register cache.  If REGNUM is -1, do
   this for all registers.  This function doesn't touch any of the
   reserved bits in *FXSAVE.  */

void
i387_fill_fxsave (void *fxsave, int regnum)
{
  struct regcache *regcache = current_regcache;
  struct gdbarch_tdep *tdep = gdbarch_tdep (current_gdbarch);
  char *regs = fxsave;
  int i;

  gdb_assert (tdep->st0_regnum >= I386_ST0_REGNUM);
  gdb_assert (tdep->num_xmm_regs > 0);

  /* Define I387_ST0_REGNUM and I387_NUM_XMM_REGS such that we use the
     proper definitions for REGCACHE's architecture.  */

#define I387_ST0_REGNUM	tdep->st0_regnum
#define I387_NUM_XMM_REGS tdep->num_xmm_regs

  for (i = I387_ST0_REGNUM; i < I387_MXCSR_REGNUM; i++)
    if (regnum == -1 || regnum == i)
      {
	/* Most of the FPU control registers occupy only 16 bits in
           the fxsave area.  Give those a special treatment.  */
	if (i >= I387_FCTRL_REGNUM && i < I387_XMM0_REGNUM
	    && i != I387_FIOFF_REGNUM && i != I387_FOOFF_REGNUM)
	  {
	    unsigned char buf[4];

	    regcache_raw_collect (regcache, i, buf);

	    if (i == I387_FOP_REGNUM)
	      {
		/* The opcode occupies only 11 bits.  Make sure we
                   don't touch the other bits.  */
		buf[1] &= ((1 << 3) - 1);
		buf[1] |= ((FXSAVE_ADDR (regs, i))[1] & ~((1 << 3) - 1));
	      }
	    else if (i == I387_FTAG_REGNUM)
	      {
		/* Converting back is much easier.  */

		unsigned short ftag;
		int fpreg;

		ftag = (buf[1] << 8) | buf[0];
		buf[0] = 0;
		buf[1] = 0;

		for (fpreg = 7; fpreg >= 0; fpreg--)
		  {
		    int tag = (ftag >> (fpreg * 2)) & 3;

		    if (tag != 3)
		      buf[0] |= (1 << fpreg);
		  }
	      }
	    memcpy (FXSAVE_ADDR (regs, i), buf, 2);
	  }
	else
	  regcache_raw_collect (regcache, i, FXSAVE_ADDR (regs, i));
      }

  if (regnum == I387_MXCSR_REGNUM || regnum == -1)
    regcache_raw_collect (regcache, I387_MXCSR_REGNUM,
			  FXSAVE_MXCSR_ADDR (regs));

#undef I387_ST0_REGNUM
#undef I387_NUM_XMM_REGS
}

/* Recreate the FTW (tag word) valid bits from the 80-bit FP data in
   *RAW.  */

static int
i387_tag (const unsigned char *raw)
{
  int integer;
  unsigned int exponent;
  unsigned long fraction[2];

  integer = raw[7] & 0x80;
  exponent = (((raw[9] & 0x7f) << 8) | raw[8]);
  fraction[0] = ((raw[3] << 24) | (raw[2] << 16) | (raw[1] << 8) | raw[0]);
  fraction[1] = (((raw[7] & 0x7f) << 24) | (raw[6] << 16)
		 | (raw[5] << 8) | raw[4]);

  if (exponent == 0x7fff)
    {
      /* Special.  */
      return (2);
    }
  else if (exponent == 0x0000)
    {
      if (fraction[0] == 0x0000 && fraction[1] == 0x0000 && !integer)
	{
	  /* Zero.  */
	  return (1);
	}
      else
	{
	  /* Special.  */
	  return (2);
	}
    }
  else
    {
      if (integer)
	{
	  /* Valid.  */
	  return (0);
	}
      else
	{
	  /* Special.  */
	  return (2);
	}
    }
}

/* Prepare the FPU stack in REGCACHE for a function return.  */

void
i387_return_value (struct gdbarch *gdbarch, struct regcache *regcache)
{
  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
  ULONGEST fstat;

  /* Define I387_ST0_REGNUM such that we use the proper
     definitions for the architecture.  */
#define I387_ST0_REGNUM tdep->st0_regnum

  /* Set the top of the floating-point register stack to 7.  The
     actual value doesn't really matter, but 7 is what a normal
     function return would end up with if the program started out with
     a freshly initialized FPU.  */
  regcache_raw_read_unsigned (regcache, I387_FSTAT_REGNUM, &fstat);
  fstat |= (7 << 11);
  regcache_raw_write_unsigned (regcache, I387_FSTAT_REGNUM, fstat);

  /* Mark %st(1) through %st(7) as empty.  Since we set the top of the
     floating-point register stack to 7, the appropriate value for the
     tag word is 0x3fff.  */
  regcache_raw_write_unsigned (regcache, I387_FTAG_REGNUM, 0x3fff);

#undef I387_ST0_REGNUM
}