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AEDIT$–ASCII Image Composition Editing Package
4.2.2. Floating-Point Editing Routines
AEDIT$F edits floating-point numbers into one of two general formats.
• Fixed decimal format (no exponent)
• Scientific format
Fixed Decimal Format
A number edited in fixed decimal format consists of a sign (if negative) followed by the
digits of the number with an embedded decimal point. The sign is present only if the
number is negative; a positive number has no sign character.
The floating-point editing routines require three parameters in addition to the address of
the floating-point packet. The first two are called x and y and are supplied in S5 and S6
of register A0. They specify the format of the edited number as described below. The
third parameter is the single- or double-precision number to be edited. If single
precision, the number is specified in A1; if double precision, the number is specified in
registers A1 and A2.
The x parameter specifies the width of the edited field; in other words, the number of
character positions that the edited number will occupy, including sign and decimal point.
If the value of x is too small to represent the value being edited, it is ignored, and as
many character positions are used as are required to correctly represent the number.
The y parameter specifies how many fractional digits will be edited. This is the number
of digits appearing to the right of the decimal point. The value of y may be any value
greater than or equal to zero, but should always be less than the value of x to allow for
the sign and decimal point characters.
The maximum number of significant digits for which the floating-point routines can
generate correct results in the fixed decimal format is 8 for single-precision numbers and
17 for double precision. It includes digits on both the sides of the decimal point. This is
because the 2200 single-precision floating-point format uses 27 bits for mantissa which
can represent up to 8 decimal digits. The double-precision floating-point format uses 60
bits for the mantissa which can represent up to 18 decimal digits. Rounding can be done
at a maximum of the 18th digit. This will provide rounded results up to 17 digits. If the
rounding option has been set with a value of y greater than 17 rounding will not be done
by these routines.
For example, the following numbers are in fixed decimal format:
258.61 Requires parameter values of x > 6 and y = 2.
-85.2239 Requires parameter values of x > 8 and y = 4.
1093. Requires parameter values of x > 5 and y = 0.
4–14 7833 1733–004