reg_constant.c

linux 内核源代码

/*---------------------------------------------------------------------------+
 |  reg_constant.c                                                           |
 |                                                                           |
 | All of the constant FPU_REGs                                              |
 |                                                                           |
 | Copyright (C) 1992,1993,1994,1997                                         |
 |                     W. Metzenthen, 22 Parker St, Ormond, Vic 3163,        |
 |                     Australia.  E-mail   [e-mail]               |
 |                                                                           |
 |                                                                           |
 +---------------------------------------------------------------------------*/

#include "fpu_system.h"
#include "fpu_emu.h"
#include "status_w.h"
#include "reg_constant.h"
#include "control_w.h"


#define MAKE_REG(s,e,l,h) { l, h, \
                            ((EXTENDED_Ebias+(e)) | ((SIGN_##s != 0)*0x8000)) }

FPU_REG const CONST_1    = MAKE_REG(POS, 0, 0x00000000, 0x80000000);
#if 0
FPU_REG const CONST_2    = MAKE_REG(POS, 1, 0x00000000, 0x80000000);
FPU_REG const CONST_HALF = MAKE_REG(POS, -1, 0x00000000, 0x80000000);
#endif  /*  0  */
static FPU_REG const CONST_L2T  = MAKE_REG(POS, 1, 0xcd1b8afe, 0xd49a784b);
static FPU_REG const CONST_L2E  = MAKE_REG(POS, 0, 0x5c17f0bc, 0xb8aa3b29);
FPU_REG const CONST_PI   = MAKE_REG(POS, 1, 0x2168c235, 0xc90fdaa2);
FPU_REG const CONST_PI2  = MAKE_REG(POS, 0, 0x2168c235, 0xc90fdaa2);
FPU_REG const CONST_PI4  = MAKE_REG(POS, -1, 0x2168c235, 0xc90fdaa2);
static FPU_REG const CONST_LG2  = MAKE_REG(POS, -2, 0xfbcff799, 0x9a209a84);
static FPU_REG const CONST_LN2  = MAKE_REG(POS, -1, 0xd1cf79ac, 0xb17217f7);

/* Extra bits to take pi/2 to more than 128 bits precision. */
FPU_REG const CONST_PI2extra = MAKE_REG(NEG, -66,
					 0xfc8f8cbb, 0xece675d1);

/* Only the sign (and tag) is used in internal zeroes */
FPU_REG const CONST_Z    = MAKE_REG(POS, EXP_UNDER, 0x0, 0x0);

/* Only the sign and significand (and tag) are used in internal NaNs */
/* The 80486 never generates one of these 
FPU_REG const CONST_SNAN = MAKE_REG(POS, EXP_OVER, 0x00000001, 0x80000000);
 */
/* This is the real indefinite QNaN */
FPU_REG const CONST_QNaN = MAKE_REG(NEG, EXP_OVER, 0x00000000, 0xC0000000);

/* Only the sign (and tag) is used in internal infinities */
FPU_REG const CONST_INF  = MAKE_REG(POS, EXP_OVER, 0x00000000, 0x80000000);


static void fld_const(FPU_REG const *c, int adj, u_char tag)
{
  FPU_REG *st_new_ptr;

  if ( STACK_OVERFLOW )
    {
      FPU_stack_overflow();
      return;
    }
  push();
  reg_copy(c, st_new_ptr);
  st_new_ptr->sigl += adj;  /* For all our fldxxx constants, we don't need to
			       borrow or carry. */
  FPU_settag0(tag);
  clear_C1();
}

/* A fast way to find out whether x is one of RC_DOWN or RC_CHOP
   (and not one of RC_RND or RC_UP).
   */
#define DOWN_OR_CHOP(x)  (x & RC_DOWN)

static void fld1(int rc)
{
  fld_const(&CONST_1, 0, TAG_Valid);
}

static void fldl2t(int rc)
{
  fld_const(&CONST_L2T, (rc == RC_UP) ? 1 : 0, TAG_Valid);
}

static void fldl2e(int rc)
{
  fld_const(&CONST_L2E, DOWN_OR_CHOP(rc) ? -1 : 0, TAG_Valid);
}

static void fldpi(int rc)
{
  fld_const(&CONST_PI, DOWN_OR_CHOP(rc) ? -1 : 0, TAG_Valid);
}

static void fldlg2(int rc)
{
  fld_const(&CONST_LG2, DOWN_OR_CHOP(rc) ? -1 : 0, TAG_Valid);
}

static void fldln2(int rc)
{
  fld_const(&CONST_LN2, DOWN_OR_CHOP(rc) ? -1 : 0, TAG_Valid);
}

static void fldz(int rc)
{
  fld_const(&CONST_Z, 0, TAG_Zero);
}

typedef void (*FUNC_RC)(int);

static FUNC_RC constants_table[] = {
  fld1, fldl2t, fldl2e, fldpi, fldlg2, fldln2, fldz, (FUNC_RC)FPU_illegal
};

void fconst(void)
{
  (constants_table[FPU_rm])(control_word & CW_RC);
}