Q28023: MS Floating Point Is Faster Than BC /FPa Alternate Math

Article: Q28023
Product(s): See article
Version(s): 6.00 6.00b 7.00  | 6.00 6.00b 7.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_basic
Last Modified: 2-FEB-1990

An EXE compiled with the Alternate Math package (BC /FPa) performs
floating-point calculations more slowly than an EXE compiled with
QuickBASIC Versions 3.00 and 2.x Microsoft Floating Point.

However, an EXE compiled with the alternate math package is between 40
and 50 percent faster than an EXE compiled with IEEE Floating Point
(with no /FPa switch) when run on a computer that does not have a
coprocessor.

Microsoft BASIC Compiler Versions 6.00 and 6.00b and Microsoft BASIC
Professional Development System (PDS) Version 7.00 do not support
Microsoft Floating Point. If you want the greatest floating-point
speed on a computer that does not have a coprocessor, compile with the
BC /FPa switch. ("FPa" stands for "Floating Point Alternate-Math
Library"). If you want the greatest floating-point speed on a computer
that has a coprocessor, compile with the BC /FPi switch. ("FPi" stands
for "Floating Point In-line Instructions"). In-line Instructions is
the default when you compile with BC and without /FPa or /FPi switch.

Microsoft Floating Point is an older format found in the
noncoprocessor version of QuickBASIC Version 3.00. It also is found in
all prior versions of QuickBASIC (Versions 2.10, 2.00, 1.02, 1.01,
1.00).

Microsoft BASIC Compiler Versions 6.00 and 6.00b and Microsoft BASIC
PDS Version 7.00 do not support Microsoft Floating Point. These
products have adopted IEEE and Alternate Math in order to be linkable
with FORTRAN, PASCAL, and C.

Compiling with BC /FPa gives you the Alternate Math floating-point
format. (The QuickBASIC interpreter uses only IEEE and cannot use
Alternate Math.)

Compiling without /FPa gives you IEEE floating-point format. IEEE
floating-point format is fastest when run on a computer that has a
coprocessor installed.

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