g_generic_x87.c

unix下调试内存泄露的工具源代码

      }
      return;
   }

   /* It's not a zero, denormal, infinity or nan.  So it must be a
      normalised number.  Rebias the exponent and build the new
      number.  */
   bexp += (16383 - 1023);

   f80[9] = toUChar( (sign << 7) | ((bexp >> 8) & 0xFF) );
   f80[8] = toUChar( bexp & 0xFF );
   f80[7] = toUChar( (1 << 7) | ((f64[6] << 3) & 0x78) 
                              | ((f64[5] >> 5) & 7) );
   f80[6] = toUChar( ((f64[5] << 3) & 0xF8) | ((f64[4] >> 5) & 7) );
   f80[5] = toUChar( ((f64[4] << 3) & 0xF8) | ((f64[3] >> 5) & 7) );
   f80[4] = toUChar( ((f64[3] << 3) & 0xF8) | ((f64[2] >> 5) & 7) );
   f80[3] = toUChar( ((f64[2] << 3) & 0xF8) | ((f64[1] >> 5) & 7) );
   f80[2] = toUChar( ((f64[1] << 3) & 0xF8) | ((f64[0] >> 5) & 7) );
   f80[1] = toUChar( ((f64[0] << 3) & 0xF8) );
   f80[0] = toUChar( 0 );
}


/* Convert an x87 extended double (80-bit) into an IEEE 754 double
   (64-bit), mimicking the hardware fairly closely.  Both numbers are
   stored little-endian.  Limitations, both of which could be fixed,
   given some level of hassle:

   * Rounding following truncation could be a bit better.

   * Identity of NaNs is not preserved.

   See comments in the code for more details.
*/
void convert_f80le_to_f64le ( /*IN*/UChar* f80, /*OUT*/UChar* f64 )
{
   Bool  isInf;
   Int   bexp, i, j;
   UChar sign;

   sign = toUChar((f80[9] >> 7) & 1);
   bexp = (((UInt)f80[9]) << 8) | (UInt)f80[8];
   bexp &= 0x7FFF;

   /* If the exponent is zero, either we have a zero or a denormal.
      But an extended precision denormal becomes a double precision
      zero, so in either case, just produce the appropriately signed
      zero. */
   if (bexp == 0) {
      f64[7] = toUChar(sign << 7);
      f64[6] = f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0;
      return;
   }
   
   /* If the exponent is 7FFF, this is either an Infinity, a SNaN or
      QNaN, as determined by examining bits 62:0, thus:
          0  ... 0    Inf
          0X ... X    SNaN
          1X ... X    QNaN
      where at least one of the Xs is not zero.
   */
   if (bexp == 0x7FFF) {
      isInf = toBool(
                 (f80[7] & 0x7F) == 0 
                 && f80[6] == 0 && f80[5] == 0 && f80[4] == 0 
                 && f80[3] == 0 && f80[2] == 0 && f80[1] == 0 
                 && f80[0] == 0
              );
      if (isInf) {
         if (0 == (f80[7] & 0x80))
            goto wierd_NaN;
         /* Produce an appropriately signed infinity:
            S 1--1 (11)  0--0 (52)
         */
         f64[7] = toUChar((sign << 7) | 0x7F);
         f64[6] = 0xF0;
         f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0;
         return;
      }
      /* So it's either a QNaN or SNaN.  Distinguish by considering
         bit 62.  Note, this destroys all the trailing bits
         (identity?) of the NaN.  IEEE754 doesn't require preserving
         these (it only requires that there be one QNaN value and one
         SNaN value), but x87 does seem to have some ability to
         preserve them.  Anyway, here, the NaN's identity is
         destroyed.  Could be improved. */
      if (f80[8] & 0x40) {
         /* QNaN.  Make a QNaN:
            S 1--1 (11)  1  1--1 (51) 
         */
         f64[7] = toUChar((sign << 7) | 0x7F);
         f64[6] = 0xFF;
         f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0xFF;
      } else {
         /* SNaN.  Make a SNaN:
            S 1--1 (11)  0  1--1 (51) 
         */
         f64[7] = toUChar((sign << 7) | 0x7F);
         f64[6] = 0xF7;
         f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0xFF;
      }
      return;
   }

   /* If it's not a Zero, NaN or Inf, and the integer part (bit 62) is
      zero, the x87 FPU appears to consider the number denormalised
      and converts it to a QNaN. */
   if (0 == (f80[7] & 0x80)) {
      wierd_NaN:
      /* Strange hardware QNaN:
         S 1--1 (11)  1  0--0 (51) 
      */
      /* On a PIII, these QNaNs always appear with sign==1.  I have
         no idea why. */
      f64[7] = (1 /*sign*/ << 7) | 0x7F;
      f64[6] = 0xF8;
      f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0;
      return;
   }

   /* It's not a zero, denormal, infinity or nan.  So it must be a 
      normalised number.  Rebias the exponent and consider. */
   bexp -= (16383 - 1023);
   if (bexp >= 0x7FF) {
      /* It's too big for a double.  Construct an infinity. */
      f64[7] = toUChar((sign << 7) | 0x7F);
      f64[6] = 0xF0;
      f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0;
      return;
   }

   if (bexp <= 0) {
      /* It's too small for a normalised double.  First construct a
         zero and then see if it can be improved into a denormal.  */
      f64[7] = toUChar(sign << 7);
      f64[6] = f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0;

      if (bexp < -52)
         /* Too small even for a denormal. */
         return;

      /* Ok, let's make a denormal.  Note, this is SLOW. */
      /* Copy bits 63, 62, 61, etc of the src mantissa into the dst, 
         indexes 52+bexp, 51+bexp, etc, until k+bexp < 0. */
      /* bexp is in range -52 .. 0 inclusive */
      for (i = 63; i >= 0; i--) {
         j = i - 12 + bexp;
         if (j < 0) break;
         /* We shouldn't really call vassert from generated code. */
         vassert(j >= 0 && j < 52);
         write_bit_array ( f64,
                           j,
                           read_bit_array ( f80, i ) );
      }
      /* and now we might have to round ... */
      if (read_bit_array(f80, 10+1 - bexp) == 1) 
         goto do_rounding;

      return;
   }

   /* Ok, it's a normalised number which is representable as a double.
      Copy the exponent and mantissa into place. */
   /*
   for (i = 0; i < 52; i++)
      write_bit_array ( f64,
                        i,
                        read_bit_array ( f80, i+11 ) );
   */
   f64[0] = toUChar( (f80[1] >> 3) | (f80[2] << 5) );
   f64[1] = toUChar( (f80[2] >> 3) | (f80[3] << 5) );
   f64[2] = toUChar( (f80[3] >> 3) | (f80[4] << 5) );
   f64[3] = toUChar( (f80[4] >> 3) | (f80[5] << 5) );
   f64[4] = toUChar( (f80[5] >> 3) | (f80[6] << 5) );
   f64[5] = toUChar( (f80[6] >> 3) | (f80[7] << 5) );

   f64[6] = toUChar( ((bexp << 4) & 0xF0) | ((f80[7] >> 3) & 0x0F) );

   f64[7] = toUChar( (sign << 7) | ((bexp >> 4) & 0x7F) );

   /* Now consider any rounding that needs to happen as a result of
      truncating the mantissa. */
   if (f80[1] & 4) /* read_bit_array(f80, 10) == 1) */ {

      /* If the bottom bits of f80 are "100 0000 0000", then the
         infinitely precise value is deemed to be mid-way between the
         two closest representable values.  Since we're doing
         round-to-nearest (the default mode), in that case it is the
         bit immediately above which indicates whether we should round
         upwards or not -- if 0, we don't.  All that is encapsulated
         in the following simple test. */
      if ((f80[1] & 0xF) == 4/*0100b*/ && f80[0] == 0)
         return;

      do_rounding:
      /* Round upwards.  This is a kludge.  Once in every 2^24
         roundings (statistically) the bottom three bytes are all 0xFF
         and so we don't round at all.  Could be improved. */
      if (f64[0] != 0xFF) { 
         f64[0]++; 
      }
      else 
      if (f64[0] == 0xFF && f64[1] != 0xFF) {
         f64[0] = 0;
         f64[1]++;
      }
      else      
      if (f64[0] == 0xFF && f64[1] == 0xFF && f64[2] != 0xFF) {
         f64[0] = 0;
         f64[1] = 0;
         f64[2]++;
      }
      /* else we don't round, but we should. */
   }
}


/*---------------------------------------------------------------*/
/*--- end                       guest-generic/h_generic_x87.c ---*/
/*---------------------------------------------------------------*/