# PGPLOT Module: PGNUMB -- convert a number into a plottable character string

SUBROUTINE PGNUMB (MM, PP, FORM, STRING, NC)
INTEGER MM, PP, FORM
CHARACTER*(*) STRING
INTEGER NC

This routine converts a number into a decimal character
representation. To avoid problems of floating-point roundoff, the
number must be provided as an integer (MM) multiplied by a power of 10
(10**PP). The output string retains only significant digits of MM,
and will be in either integer format (123), decimal format (0.0123),
or exponential format (1.23x10**5). Standard escape sequences \u, \d
raise the exponent and \x is used for the multiplication sign.
This routine is used by PGBOX to create numeric labels for a plot.

Formatting rules:
(a) Decimal notation (FORM=1):
- Trailing zeros to the right of the decimal sign are
omitted
- The decimal sign is omitted if there are no digits
to the right of it
- When the decimal sign is placed before the first digit
of the number, a zero is placed before the decimal sign
- The decimal sign is a period (.)
- No spaces are placed between digits (ie digits are not
grouped in threes as they should be)
- A leading minus (-) is added if the number is negative
(b) Exponential notation (FORM=2):
- The exponent is adjusted to put just one (non-zero)
digit before the decimal sign
- The mantissa is formatted as in (a), unless its value is
1 in which case it and the multiplication sign are omitted
- If the power of 10 is not zero and the mantissa is not
zero, an exponent of the form \x10\u[-]nnn is appended,
where \x is a multiplication sign (cross), \u is an escape
sequence to raise the exponent, and as many digits nnn
are used as needed
(c) Automatic choice (FORM=0):
Decimal notation is used if the absolute value of the
number is less than 10000 or greater than or equal to
0.01. Otherwise exponential notation is used.

Arguments
MM (input)
PP (input) : the value to be formatted is MM*10**PP.
FORM (input) : controls how the number is formatted:
FORM = 0 -- use either decimal or exponential
FORM = 1 -- use decimal notation
FORM = 2 -- use exponential notation
STRING (output) : the formatted character string, left justified.
If the length of STRING is insufficient, a single
asterisk is returned, and NC=1.
NC (output) : the number of characters used in STRING:
the string to be printed is STRING(1:NC).