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Q38274: Single Precision "Overflow" when Nearing Divide By Zero;10E-38

Article: Q38274
Product(s): See article
Version(s): 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 9-DEC-1988

The code example below produces an "OVERFLOW" error at n = 38 for
QuickBASIC Versions 3.00, 4.00, and 4.00b, and BASIC Compiler Versions
6.00 and 6.00b for MS-DOS and OS/2. The overflow occurs as you divide
by ever larger numbers and approach the limits of the negative
exponent for single precision. The program may overflow at different
places in other versions of BASIC. To work around the "Overflow"
error, use at least one double precision variable or constant in the
expression before assigning to the variable.

The following code example gives an "Overflow" error at n = 38:

FOR n = 1 TO 100
 x# = 1 / 10 ^ n
 PRINT n, x#
NEXT

In the above program, the expression 1/10^n is optimized to use single
precision, since the most precise argument in the expression is n,
which defaults to single precision.

To avoid the overflow of the negative single precision exponent,
change n to double precision (n#). This forces the expression 1/10^n#
to be stored in a double precision temporary storage area before being
assigned to x#:

FOR n# = 1 TO 100  ' This program runs fine from n#=1 through 100.
 x# = 1 / 10 ^ n#
 PRINT n#, x#
NEXT

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