Help for IFTHEN

PURPOSE

Ifthen allows the user to perform if-then-else constructs
on columns of data in an ibis tabular file.

There are 3 string parameter functions for the program, 
IF, THEN and ELSE. They use math and logical expressions
to perform column manipulations. The default options
for the THEN and ELSE parameters are NOOP, meaning
perform no operations.

MATH AND FUNCTIONS

The math functions available are: @sqrt, @alog, @alog10,
@aint, @sin, @cos, @tan, @asin, @acos, @atan,
@atan2, @abs, @min, @max, @mod.

Standard binary operations are: +,- *, / and ^ (pow).

Logic operations <, >, <=, >=, ==, !=, && (and), || (or),
and ! (not).  The main difference with C vs the FORTRAN
conventions used by program MF is the use of ^ for power
of two integers or reals.

Note 1: ^^ (xor) is not implemented (use (a||b)&&(!(a&&b))).

Note 2: The old FORTRAN constructs .EQ., .NE. and **
are no longer allowed.

Note 3: When && is entered in a function, the internal
print shows only 1 &. Thats because TAE uses & for variable
names and traps it out. Putting in 3 & shows the correct
&& in the function. It doesnt realy matter, the function
is evaluated properly.

ABOUT MATH AND LOGIC OPERATORS IN FUCTION STATEMENTS

You need to be careful about 2 operators following each
other.  They can lead to incorrect code and not give
warnings about what is happening. You should be especially
careful about occurences where negative numbers might
inadvertently enter into the function.  This might happen
in scripts where a large number of ifthen calls are being
made.

Suppose you have a then function like
       then=("c4=(c3 > &sigtest)")             (1)
                                                                                                                             
As long as sigtest is a positive number everything proceeds
OK, but if it is negative than what you will have is

       then=("c4=(c3 > -&sigtest)")            (2)
                                                                                                                             
Internally this is translated into two operators and will
give bad results.
                                                                                                                             
Therefore, if neg numbers are possible then the function
should be written
                                                                                                                             
       then=("c4=(c3 > (&sigtest))")           (3)

See documentation for mf3 for more information on function
parsing.

If you forget then the program will terminate with the following
message:

ifthen  ibis.tbl if=("(c12==1") then=("c15=-1.538559496403e-01") else=("c15=C15")
if   string = (c12==1
then string = c15=-1.538559496403e-01
else string = c15=C15
??E stsget: illegal symbol [
??E program terminating
 ** ABEND called **

(Not a very good message, I'll grant you).

METHOD

    IFTHEN performs arithmetic operations on an interface file.
    The  program  uses  two  library  routines SP_KNUTH  and
    SP_XKNUTH,   to   compile  and  interpret  C-like
    expressions  entered by the parameters in an expression
    such as:

           IF=("(100*C34)/C4")  THEN=("C135=17") ELSE=("C135=0")

    In this expression,  C34 and C4 are columns used in the
    test (IF) function. If the IF expression is evaluated as
    TRUE (i.e., == 1) then the THEN expression is put in C135.
    IF the IF expression is evaluated as FALSE (i.e., == 0),
    then the ELSE expression is put in C135.

    Notice that no single = is placed in the IF function.
    Equalities are expressed as == just like in C.

    If you need an equals sign then uses expressions like:

        IF=("C100==12") THEN=("C135=17") ELSE=("C135=0")

    However, internal expressions are evaluated as DOUBLE and
    so doing this can be dicey, at best.

    There is no requirement for the THEN and ELSE functions
    to evaluate to the same column.

        IF=("C100>12") THEN=("C135=17") ELSE=("C136=17")

    is legal.
 

     SP_KNUTH    compiles   the   expression   into  pseudo-machine
     instructions.   The  expression is applied to the input
     columns in SP_XKNUTH to produce the output column, C135.
                                                                                                                            
RESTRICTIONS

1.     Maximum number of columns in one execution is 100. (oops, 9 until bug is fixed)
2.     The number of columns in the IBIS file is not limited here.
3.     Maximum input string length is 10,000 (40 x 250).
4.     Maximum number of operations is 3000.
5.     Maximum number of temp locations is 938.
6.     Maximum number of constants from the expression is 960.
7.     Operators must be separated by parentheses.

notes:
                                                                                                                             
1.  Column numbers greater than 100 are mapped sequentially 1,2,3...
    so there is no limit on the number of columns in the IBIS file.
3.  The input parameter is a string array (40) each with 250 chars.
    The array is concatenated by the program into a single array.
4.  These can be counted by setting debug to one and counting the
    lines that begin with "xknuth:op,opnd".  The count is not
    easily determined by looking at a long input.
5.  These can be counted by setting debug to one and counting the
    lines that begin with "xknuth:op,opnd" and having an opnd
    value above 1061.  The count is not easily determined by
    looking at a long input.
6.  These can be counted in the input, or by setting debug to one
    and counting the lines that begin with "xknuth:op,opnd" and
    having an opnd value between 103 and 1061, inclusive.
                                                                                                                             
EXAMPLES
                                                                                                                             
     IFTHEN INP=FILE.INT if=("c3>(&sigtest)") then=("c4=(&xthresh)") else=("c4=(c1*(c1>0))")
                                                                                                                             
                                                                                                                             




TAE COMMAND LINE FORMAT

     IFTHEN INP=int PARAMS

     where
     
     int                 is a random access file.  Since it
                         is used for both input and  output,
                         no output file is specified.
     PARAMS              is   a  standard  VICAR   parameter
                         field.

    IF is a string of math or logical operations
    given in examples below.

    THEN is a string of math or logical operations
    given in examples below.

    ELSE is a string of math or logical operations (or noop)
    given in examples below.

    The DEBUG parameter will show the pseudo instructions for
    math and logic functions that arise from the
    internal routine sp_xknuth as well as other information.

    The CODE parameter will show the pseudo instructions for
    math and logic functions. The nmenomics are the same
    as for the CODE parameter for mf3 but have different
    operands for program mf.


HISTORY

Original Programmer:  R. J. Bambery - Oct 25, 2007

Revision:
  2008-02-24 - R.J. Bambery - For Linux - remove a bad strcpy
               for combining thenfunction with elsefunction
  2008-02-27 - R.J. Bambery - Fixes for ANSI_C compiler
  2008-06-19 - R.J. Bambery  - Error elaboration in pdf
  2008-07-27 - R.J. Bambery - Merged solaris pdf with linux pdf
  2008-07-28 - R.J. Bambery - Made compatible with linux afids 5b
  2008-08-20 - R.J. Bambery - Fixed bug in fstorecd which caused
               incorrect packing of double into unsigned chars
  2010-01-29 - R.J. Bambery - Made compatible with 64-bit afids Build 793      
               Linux, MacOSX (both Intel/PowerPC)          
  2011-05-05 - R.J. Bambery - Removed all warning messages generated from gcc 4.4.4
               Build 1009
  2011-06-20 - R.J. Bambery - Fixed warning messages with gcc 4.5.2 on macosx
  2012-06-06 - R.J. Bambery - initialize a variable
  2012-06-22 - R.J. Bambery - comment out an include p1proto.h. It is used
               in cartlab to define zmve
  2012-12-09 - R.J. Bambery - remove unused variables ptr, mxddwid
  2015-11-05 - W.L. Bunch - Migrated to MIPL