HP UX Performance Tools manual 201

Environmental inquiry F_SFPINFO/F_DFPINFO

Table 2-1describes floating point parameters and values returned by FPINFO.

Table 2-1	FPINFO return values
Floating	Fortran77 named	Description		Value in		Value in IEEE
point
	constant		IEEE single				double
parameter
BASE	BLAS_BASE	Base of machine	2			2
T	BLAS_T	Number of digits	24			53
		Equals 1 when proper rounding
RND	BLAS_RND	occurs in addition. Otherwise,	1			1
		equals 0
		Equals 1 when rounding in
IEEE	BLAS_IEEE	addition is IEEE style.	1			1
		Otherwise, equals 0
EMIN	BLAS_EMIN	Minimum exponent before	-126			-1022
		(gradual) underflow
EMAX	BLAS_EMAX	Minimum exponent before	127			1023
		overflow
		Machine epsilon
EPS	BLAS_EPS	EPS = 0.5BASE1 – T if RND = 1	2–24≈ 5e – 8			2–53≈ 1e – 16
		EPS = BASE1 – T if RND = 0
PREC	BLAS_PREC	EPS*BASE	2 -23			2 -52
UN	BLAS_UNDERFLOW	Underflow threshold
		= BASEEMIN	2–126≈ 1e – 38			2–1022≈ 1e – 308
OV	BLAS_OVERFLOW	Overflow threshold
		= BASEEMAX + 1 ⋅ (1 – EPS)	2128 ≈ 1e38			21024 ≈ 1e308
		Safe minimum, such that
		1 ⁄ SFMIN does not overflow.
SFMIN	BLAS_SFMIN	If 1 ⁄ OV < UN, SFMIN = UN.	2	–126	≈ 1e – 38	2	–1022	≈ 1e – 308
		Otherwise,
		SFMIN = (1+EPS) / OV

Chapter 2 Basic Vector Operations 173