static void
f2xm1(void)
{
switch (FPU_st0_tag) {
case TW_Valid:
{
FPU_REG rv, tmp;
#ifdef DENORM_OPERAND
if ((FPU_st0_ptr->exp <= EXP_UNDER) && (denormal_operand()))
return;
#endif /* DENORM_OPERAND */
if (FPU_st0_ptr->sign == SIGN_POS) {
/* poly_2xm1(x) requires 0 < x < 1. */
if (poly_2xm1(FPU_st0_ptr, &rv))
return; /* error */
reg_mul(&rv, FPU_st0_ptr, FPU_st0_ptr, FULL_PRECISION);
} else {
/* **** Should change poly_2xm1() to at least handle numbers near 0 */
/* poly_2xm1(x) doesn't handle negative
* numbers. */
/* So we compute (poly_2xm1(x+1)-1)/2, for -1
* < x < 0 */
reg_add(FPU_st0_ptr, &CONST_1, &tmp, FULL_PRECISION);
poly_2xm1(&tmp, &rv);
reg_mul(&rv, &tmp, &tmp, FULL_PRECISION);
reg_sub(&tmp, &CONST_1, FPU_st0_ptr, FULL_PRECISION);
FPU_st0_ptr->exp--;
if (FPU_st0_ptr->exp <= EXP_UNDER)
arith_underflow(FPU_st0_ptr);
}
return;
}
case TW_Zero:
return;
case TW_Infinity:
if (FPU_st0_ptr->sign == SIGN_NEG) {
/* -infinity gives -1 (p16-10) */
reg_move(&CONST_1, FPU_st0_ptr);
FPU_st0_ptr->sign = SIGN_NEG;
}
return;
default:
single_arg_error();
}
}
static void f2xm1(FPU_REG *st0_ptr, u_char tag)
{
FPU_REG a;
clear_C1();
if ( tag == TAG_Valid )
{
/* For an 80486 FPU, the result is undefined if the arg is >= 1.0 */
if ( exponent(st0_ptr) < 0 )
{
denormal_arg:
FPU_to_exp16(st0_ptr, &a);
/* poly_2xm1(x) requires 0 < st(0) < 1. */
poly_2xm1(getsign(st0_ptr), &a, st0_ptr);
}
set_precision_flag_up(); /* 80486 appears to always do this */
return;
}
if ( tag == TAG_Zero )
return;
if ( tag == TAG_Special )
tag = FPU_Special(st0_ptr);
switch ( tag )
{
case TW_Denormal:
if ( denormal_operand() < 0 )
return;
goto denormal_arg;
case TW_Infinity:
if ( signnegative(st0_ptr) )
{
/* -infinity gives -1 (p16-10) */
FPU_copy_to_reg0(&CONST_1, TAG_Valid);
setnegative(st0_ptr);
}
return;
default:
single_arg_error(st0_ptr, tag);
}
}
static void f2xm1(FPU_REG *st0_ptr, u_char tag)
{
FPU_REG a;
clear_C1();
if (tag == TAG_Valid) {
if (exponent(st0_ptr) < 0) {
denormal_arg:
FPU_to_exp16(st0_ptr, &a);
poly_2xm1(getsign(st0_ptr), &a, st0_ptr);
}
set_precision_flag_up();
return;
}
if (tag == TAG_Zero)
return;
if (tag == TAG_Special)
tag = FPU_Special(st0_ptr);
switch (tag) {
case TW_Denormal:
if (denormal_operand() < 0)
return;
goto denormal_arg;
case TW_Infinity:
if (signnegative(st0_ptr)) {
FPU_copy_to_reg0(&CONST_1, TAG_Valid);
setnegative(st0_ptr);
}
return;
default:
single_arg_error(st0_ptr, tag);
}
}
