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<TITLE>HPL_dlamch HPL 2.0 Library Functions September 10, 2008</TITLE> |
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<H1>Name</H1> |
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<B>HPL_dlamch</B> determines machine-specific arithmetic constants. |
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<H1>Synopsis</H1> |
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<CODE>#include "hpl.h"</CODE><BR><BR> |
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<CODE>double</CODE> |
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<CODE>HPL_dlamch(</CODE> |
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<CODE>const HPL_T_MACH</CODE> |
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<CODE>CMACH</CODE> |
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<CODE>);</CODE> |
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<H1>Description</H1> |
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<B>HPL_dlamch</B> |
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determines machine-specific arithmetic constants such as |
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the relative machine precision (eps), the safe minimum (sfmin) such |
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that 1 / sfmin does not overflow, the base of the machine (base), the |
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precision (prec), the number of (base) digits in the mantissa (t), |
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whether rounding occurs in addition (rnd=1.0 and 0.0 otherwise), the |
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minimum exponent before (gradual) underflow (emin), the underflow |
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threshold (rmin) base**(emin-1), the largest exponent before overflow |
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(emax), the overflow threshold (rmax) (base**emax)*(1-eps). |
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<H1>Arguments</H1> |
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<PRE>
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CMACH (local input) const HPL_T_MACH |
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Specifies the value to be returned by HPL_dlamch |
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= HPL_MACH_EPS, HPL_dlamch := eps (default) |
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= HPL_MACH_SFMIN, HPL_dlamch := sfmin |
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= HPL_MACH_BASE, HPL_dlamch := base |
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= HPL_MACH_PREC, HPL_dlamch := eps*base |
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= HPL_MACH_MLEN, HPL_dlamch := t |
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= HPL_MACH_RND, HPL_dlamch := rnd |
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= HPL_MACH_EMIN, HPL_dlamch := emin |
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= HPL_MACH_RMIN, HPL_dlamch := rmin |
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= HPL_MACH_EMAX, HPL_dlamch := emax |
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= HPL_MACH_RMAX, HPL_dlamch := rmax |
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where |
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eps = relative machine precision, |
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sfmin = safe minimum, |
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base = base of the machine, |
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prec = eps*base, |
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t = number of digits in the mantissa, |
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rnd = 1.0 if rounding occurs in addition, |
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emin = minimum exponent before underflow, |
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rmin = underflow threshold, |
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emax = largest exponent before overflow, |
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rmax = overflow threshold. |
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</PRE>
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<H1>Example</H1> |
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<CODE>#include "hpl.h"</CODE><BR><BR> |
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<PRE>
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int main(int argc, char *argv[]) |
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{
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double eps; |
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eps = HPL_dlamch( HPL_MACH_EPS ); |
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printf("eps=%18.8e\n", eps);
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exit(0); return(0); |
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} |
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</PRE>
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<H1>References</H1> |
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This function has been manually translated from the Fortran 77 LAPACK |
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auxiliary function dlamch.f (version 2.0 -- 1992), that was itself |
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based on the function ENVRON by Malcolm and incorporated suggestions |
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by Gentleman and Marovich. See |
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Malcolm M. A., Algorithms to reveal properties of floating-point |
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arithmetic., Comms. of the ACM, 15, 949-951 (1972). |
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Gentleman W. M. and Marovich S. B., More on algorithms that reveal |
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properties of floating point arithmetic units., Comms. of the ACM, |
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17, 276-277 (1974). |
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