USING THE ARBITRARY PRECISION ROUTINES IN A C PROGRAM

Part of the calc release consists of an arbitrary precision math link library.
This link library is used by the calc program to perform its own calculations.
If you wish, you can ignore the calc program entirely and call the arbitrary
precision math routines from your own C programs.

The link library is called libcalc.a, and provides routines to handle arbitrary
precision arithmetic with integers, rational numbers, or complex numbers.
There are also many numeric functions such as factorial and gcd, along
with some transcendental functions such as sin and exp.

Take a look at the sample sub-directory.  It contains a few simple
examples of how to use libcalc.a that might be helpful to look at
after you have read this file.

------------------
FIRST THINGS FIRST
------------------

...............................................................................
.                                                                             .
. You MUST call libcalc_call_me_first() prior to using libcalc lib functions! .
.                                                                             .
...............................................................................

The function libcalc_call_me_first() takes no args and returns void.  You
need call libcalc_call_me_first() only once.

-------------
INCLUDE FILES
-------------

To use any of these routines in your own programs, you need to include the
appropriate include file.  These include files are:

        zmath.h         (for integer arithmetic)
        qmath.h         (for rational arithmetic)
        cmath.h         (for complex number arithmetic)

You never need to include more than one of the above files, even if you wish
to use more than one type of arithmetic, since qmath.h automatically includes
zmath.h, and cmath.h automatically includes qmath.h.

The prototypes for the available routines are listed in the above include
files.  Some of these routines are meant for internal use, and so aren't
convenient for outside use.  So you should read the source for a routine
to see if it really does what you think it does.  I won't guarantee that
obscure internal routines won't change or disappear in future releases!

When calc is installed, all of libraries are installed into /usr/local/lib.
All of the calc header files are installed under ${INCDIRCALC}.

If CALC_SRC is defined, then the calc header files will assume that
they are in or under the current directory.  However, most external
programs most likely will not be located under calc'c source tree.
External programs most likely want to use the installed calc header
files under ${INCDIRCALC}.  External programs most likely NOT want
to define CALC_SRC.

You need to include the following file to get the symbols and variables
related to error handling:

        lib_calc.h

External programs may want to compile with:

        -I${INCDIR} -L/usr/local/lib -lcalc

If custom functions are also used, they may want to compile with:

        -I${INCDIR} -L/usr/local/lib -lcalc -lcustcalc

The CALC_SRC symbol should NOT be defined by default.  However if you are
feeling pedantic you may want to force CALC_SRC to be undefined:

        -UCALC_SRC

as well.

-------------------
MATH ERROR HANDLING
-------------------

The math_error() function is called by the math routines on an error
condition, such as malloc failures, division by zero, or some form of
an internal computation error.  The routine is called in the manner of
printf, with a format string and optional arguments:

            void math_error(char *fmt, ...);

Your program must handle math errors in one of three ways:

    1) Print the error message and then exit

        There is a math_error() function supplied with the calc library.
        By default, this routine simply prints a message to stderr and
        then exits.  By simply linking in this link library, any calc
        errors will result in a error message on stderr followed by
        an exit.

    2) Use setjmp and longjmp in your program

        Use setjmp at some appropriate level in your program, and let
        the longjmp in math_error() return to that level and to allow you
        to recover from the error.  This is what the calc program does.

        If one sets up calc_matherr_jmpbuf, and then sets
        calc_use_matherr_jmpbuf to non-zero then math_error() will
        longjmp back with the return value of calc_use_matherr_jmpbuf.
        In addition, the last calc error message will be found in
        calc_err_msg; this error is not printed to stderr.  The calc
        error message will not have a trailing newline.

        For example:

            #include <setjmp.h>
            #include "lib_calc.h"

            int error;

            ...

            if ((error = setjmp(calc_matherr_jmpbuf)) != 0) {

                    /* report the error */
                    printf("Ouch: %s\n", calc_err_msg);

                    /* reinitialize calc after the longjmp */
                    reinitialize();
            }
            calc_use_matherr_jmpbuf = 1;

        If calc_use_matherr_jmpbuf is non-zero, then the jmp_buf value
        calc_matherr_jmpbuf must be initialized by the setjmp() function
        or your program will crash.

    3) Supply your own math_error function:

            void math_error(char *fmt, ...);

        Your math_error() function may exit or transfer control to outside
        of the calc library, but it must never return or calc will crash.

External programs can obtain the appropriate calc symbols by compiling with:

        -I${INCDIR} -L/usr/local/lib -lcalc

-------------------------
PARSE/SCAN ERROR HANDLING
-------------------------

The scanerror() function is called when calc encounters a parse/scan
error.  For example, scanerror() is called when calc is given code
with a syntax error.

The variable, calc_print_scanerr_msg, controls if calc prints to stderr,
any parse/scan errors.  By default, this variable it set to 1 and so
parse/scan errors are printed to stderr.  By setting this value to zero,
parse/scan errors are not printed:

        #include "lib_calc.h"

        /* do not print parse/scan errors to stderr */
        calc_print_scanerr_msg = 0;

The last calc math error or calc parse/scan error message is kept
in the NUL terminated buffer:

        char calc_err_msg[MAXERROR+1];

The value of calc_print_scanerr_msg does not change the use
of the calc_err_msg[] buffer.  Messages are stored in that
buffer regardless of the calc_print_scanerr_msg value.

The calc_print_scanerr_msg and the calc_err_msg[] buffer are declared
lib_calc.h include file.  The initialized storage for these variables
comes from the calc library.  The MAXERROR symbol is also declared in
the lib_calc.h include file.

Your program must handle parse/scan errors in one of two ways:

    1) exit on error

        If you do not setup the calc_scanerr_jmpbuf, then when calc
        encounters a parse/scan error, a message will be printed to
        stderr and calc will exit.

    2) Use setjmp and longjmp in your program

        Use setjmp at some appropriate level in your program, and let
        the longjmp in scanerror() return to that level and to allow you
        to recover from the error.  This is what the calc program does.

        If one sets up calc_scanerr_jmpbuf, and then sets
        calc_use_scanerr_jmpbuf to non-zero then scanerror() will longjmp
        back with the return with a non-zero code.  In addition, the last
        calc error message will be found in calc_err_msg[]; this error is
        not printed to stderr.  The calc error message will not have a
        trailing newline.

        For example:

            #include <setjmp.h>
            #include "lib_calc.h"

            int scan_error;

            ...

            /* delay the printing of the parse/scan error */
            calc_use_scanerr_jmpbuf = 0;        /* this is optional */

            if ((scan_error = setjmp(calc_scanerr_jmpbuf)) != 0) {

                    /* report the parse/scan */
                    if (calc_use_scanerr_jmpbuf == 0) {
                            printf("parse error: %s\n", calc_err_msg);
                    }

                    /* initialize calc after the longjmp */
                    initialize();
            }
            calc_use_scanerr_jmpbuf = 1;

        If calc_use_scanerr_jmpbuf is non-zero, then the jmp_buf value
        calc_scanerr_jmpbuf must be initialized by the setjmp() function
        or your program will crash.

External programs can obtain the appropriate calc symbols by compiling with:

        -I${INCDIR} -L/usr/local/lib -lcalc

---------------------------
PARSE/SCAN WARNING HANDLING
---------------------------

Calc parse/scan warning message are printed to stderr by the warning()
function.  The routine is called in the manner of printf, with a format
string and optional arguments:

        void warning(char *fmt, ...);

The variable, calc_print_scanwarn_msg, controls if calc prints to stderr,
any parse/scan warnings.  By default, this variable it set to 1 and so
parse/scan warnings are printed to stderr.  By setting this value to zero,
parse/scan warnings are not printed:

        #include "lib_calc.h"

        /* do not print parse/scan warnings to stderr */
        calc_print_scanwarn_msg = 0;

The last calc calc parse/scan warning message is kept in the NUL
terminated buffer:

        char calc_warn_msg[MAXERROR+1];

The value of calc_print_scanwarn_msg does not change the use
of the calc_warn_msg[] buffer.  Messages are stored in that
buffer regardless of the calc_print_scanwarn_msg value.

Your program must handle parse/scan warnings in one of two ways:

    1) print the warning to stderr and continue

        The warning() from libcalc prints warning messages to
        stderr and returns.  The flow of execution is not changed.
        This is what calc does by default.

    2) Supply your own warning function:

            void warning(char *fmt, ...);

        Your warning function should simply return when it is finished.

External programs can obtain the appropriate calc symbols by compiling with:

        -I${INCDIR} -L/usr/local/lib -lcalc


---------------
OUTPUT ROUTINES
---------------

The output from the routines in the link library normally goes to stdout.
You can divert that output to either another FILE handle, or else
to a string.  Read the routines in zio.c to see what is available.
Diversions can be nested.

You use math_setfp to divert output to another FILE handle.  Calling
math_setfp with stdout restores output to stdout.

Use math_divertio to begin diverting output into a string.  Calling
math_getdivertedio will then return a string containing the output, and
clears the diversion.  The string is reallocated as necessary, but since
it is in memory, there are obviously limits on the amount of data that can
be diverted into it.  The string needs freeing when you are done with it.

Calling math_cleardiversions will clear all the diversions to strings, and
is useful on an error condition to restore output to a known state.  You
should also call math_setfp on errors if you had changed that.

If you wish to mix your own output with numeric output from the math routines,
then you can call math_chr, math_str, math_fill, math_fmt, or math_flush.
These routines output single characters, output null-terminated strings,
output strings with space filling, output formatted strings like printf, and
flush the output.  Output from these routines is diverted as described above.

You can change the default output mode by calling math_setmode, and you can
change the default number of digits printed by calling math_setdigits.  These
routines return the previous values.  The possible modes are described in
zmath.h.

--------------
USING INTEGERS
--------------

The arbitrary precision integer routines define a structure called a ZVALUE.
This is defined in zmath.h.  A ZVALUE contains a pointer to an array of
integers, the length of the array, and a sign flag.  The array is allocated
using malloc, so you need to free this array when you are done with a
ZVALUE.  To do this, you should call zfree() with the ZVALUE as an argument
and never try to free the array yourself using free().  The reason for this
is that sometimes the pointer points to a statically allocated arrays which
should NOT be freed.

The ZVALUE structures are passed to routines by value, and are returned
through pointers.  For example, to multiply two small integers together,
you could do the following:

        ZVALUE  z1, z2, z3;

        itoz(3L, &z1);
        itoz(4L, &z2);
        zmul(z1, z2, &z3);

Use zcopy to copy one ZVALUE to another.  There is no sharing of arrays
between different ZVALUEs even if they have the same value, so you MUST
use this routine.  Simply assigning one value into another will cause
problems when one of the copies is freed.  However, the special ZVALUE
values _zero_ and _one_ CAN be assigned to variables directly, since their
values of 0 and 1 are so common that special checks are made for them.

For initial values besides 0 or 1, you need to call itoz to convert a long
value into a ZVALUE, as shown in the above example.  Or alternatively,
for larger numbers you can use the str2z routine to convert a string which
represents a number into a ZVALUE.  The string can be in decimal, octal,
hex, or binary according to the leading digits.

Always make sure you free a ZVALUE when you are done with it or when you
are about to overwrite an old ZVALUE with another value by passing its
address to a routine as a destination value, otherwise memory will be
lost.  The following shows an example of the correct way to free memory
over a long sequence of operations.

        ZVALUE z1, z2, z3;

        z1 = _one_;
        str2z("12345678987654321", &z2);
        zadd(z1, z2, &z3);
        zfree(z1);
        zfree(z2);
        zsquare(z3, &z1);
        zfree(z3);
        itoz(17L, &z2);
        zsub(z1, z2, &z3);
        zfree(z1);
        zfree(z2);
        zfree(z3);

There are some quick checks you can make on integers.  For example, whether
or not they are zero, negative, even, and so on.  These are all macros
defined in zmath.h, and should be used instead of checking the parts of the
ZVALUE yourself.  Examples of such checks are:

        ziseven(z)      (number is even)
        zisodd(z)       (number is odd)
        ziszero(z)      (number is zero)
        zisneg(z)       (number is negative)
        zispos(z)       (number is positive)
        zisunit(z)      (number is 1 or -1)
        zisone(z)       (number is 1)
        zisnegone(z)    (number is -1)
        zistwo(z)       (number is 2)
        zisabstwo(z)    (number is 2 or -2)
        zisabsleone(z)  (number is -1, 0 or 1)
        zislezero(z)    (number is <= 0)
        zisleone(z)     (number is <= 1)
        zge16b(z)       (number is >= 2^16)
        zge24b(z)       (number is >= 2^24)
        zge31b(z)       (number is >= 2^31)
        zge32b(z)       (number is >= 2^32)
        zge64b(z)       (number is >= 2^64)

Typically the largest unsigned long is typedefed to FULL.  The following
macros are useful in dealing with this data type:

        MAXFULL         (largest positive FULL value)
        MAXUFULL        (largest unsigned FULL value)
        zgtmaxfull(z)   (number is > MAXFULL)
        zgtmaxufull(z)  (number is > MAXUFULL)
        zgtmaxlong(z)   (number is > MAXLONG, largest long value)
        zgtmaxulong(z)  (number is > MAXULONG, largest unsigned long value)

If zgtmaxufull(z) is false, then one may quickly convert the absolute
value of number into a full with the macro:

        ztofull(z)      (convert abs(number) to FULL)
        ztoulong(z)     (convert abs(number) to an unsigned long)
        ztolong(z)      (convert abs(number) to a long)

If the value is too large for ztofull(), ztoulong() or ztolong(), only
the low order bits converted.

There are two types of comparisons you can make on ZVALUEs.  This is whether
or not they are equal, or the ordering on size of the numbers.  The zcmp
function tests whether two ZVALUEs are equal, returning true if they differ.
The zrel function tests the relative sizes of two ZVALUEs, returning -1 if
the first one is smaller, 0 if they are the same, and 1 if the first one
is larger.

To determine if z is an integer power of 2, use zispowerof2:

        ZVALUE z;               /* value to check if it is a power of */
        FULL log2;              /* set to log base 2 of z when is_power_of_2 is true */
        bool is_power_of_2;

        is_power_of_2 = zispowerof2(z, &log2)

Returns true if z an integer power of 2: set log2 to log base 2 of z.
Returns false if z is NOT integer power of 2 and leave log2 untouched.
The log2 arg must be a non-NULL pointer to a ZVALUE.

---------------
USING FRACTIONS
---------------

The arbitrary precision fractional routines define a structure called NUMBER.
This is defined in qmath.h.  A NUMBER contains two ZVALUEs for the numerator
and denominator of a fraction, and a count of the number of uses there are
for this NUMBER.  The numerator and denominator are always in lowest terms,
and the sign of the number is contained in the numerator.  The denominator
is always positive.  If the NUMBER is an integer, the denominator has the
value 1.

Unlike ZVALUEs, NUMBERs are passed using pointers, and pointers to them are
returned by functions.  So the basic type for using fractions is not really
(NUMBER), but is (NUMBER *).  NUMBERs are allocated using the qalloc routine.
This returns a pointer to a number which has the value 1.  Because of the
special property of a ZVALUE of 1, the numerator and denominator of this
returned value can simply be overwritten with new ZVALUEs without needing
to free them first.  The following illustrates this:

        NUMBER *q;

        q = qalloc();
        itoz(55L, &q->num);

A better way to create NUMBERs with particular values is to use the itoq,
iitoq, or str2q functions.  Using itoq makes a long value into a NUMBER,
using iitoq makes a pair of longs into the numerator and denominator of a
NUMBER (reducing them first if needed), and str2q converts a string representing
a number into the corresponding NUMBER.  The str2q function accepts input in
integral, fractional, real, or exponential formats.  Examples of allocating
numbers are:

        NUMBER *q1, *q2, *q3, *q4;

        q1 = itoq(66L);
        q2 = iitoq(2L, 3L);
        q3 = str2q("456.78");
        q4 = utoq((FULL) 1234567890L);

Also unlike ZVALUEs, NUMBERs are quickly copied.  This is because they contain
a link count, which is the number of pointers there are to the NUMBER.  The
qlink macro is used to copy a pointer to a NUMBER, and simply increments
the link count and returns the same pointer.  Since it is a macro, the
argument should not be a function call, but a real pointer variable.  The
qcopy routine will actually make a new copy of a NUMBER, with a new link
count of 1.  This is not usually needed.

NUMBERs are deleted using the qfree routine.  This decrements the link count
in the NUMBER, and if it reaches zero, then it will deallocate both of
the ZVALUEs contained within the NUMBER, and then puts the NUMBER structure
onto a free list for quick reuse.  The following is an example of allocating
NUMBERs, copying them, adding them, and finally deleting them again.

        NUMBER *q1, *q2, *q3, *q4;

        q1 = itoq(111L);
        q2 = qlink(q1);
        q3 = qqadd(q1, q2);
        q4 = qnum(q2, q3);

        qfree(q1);
        qfree(q2);
        qfree(q3);

Because of the passing of pointers and the ability to copy numbers easily,
you might wish to use the rational number routines even for integral
calculations.  They might be slightly slower than the raw integral routines,
but are more convenient to program with.

The prototypes for the fractional routines are defined in qmath.h.
Many of the definitions for integer functions parallel the ones defined
in zmath.h.  But there are also functions used only for fractions.
Examples of these are qnum to return the numerator, qden to return the
denominator, qint to return the integer part of, qfrac to return the
fractional part of, and qinv to invert a fraction.

There are some transcendental functions in the link library, such as sin
and cos.  These cannot be evaluated exactly as fractions.  Therefore,
they accept another argument which tells how accurate you want the result.
This is an "epsilon" value, and the returned value will be within that
quantity of the correct value.  This is usually an absolute difference,
but for some functions (such as exp), this is a relative difference.
For example, to calculate sin(0.5) to 100 decimal places, you could do:

        NUMBER *q, *ans, *epsilon;

        q = str2q("0.5");
        epsilon = str2q("1e-100");
        ans = qsin(q, epsilon);

There are many convenience macros similar to the ones for ZVALUEs which can
give quick information about NUMBERs.  In addition, there are some new ones
applicable to fractions.  These are all defined in qmath.h.  Some of these
macros are:

        qiszero(q)              (number is zero)
        qisneg(q)               (number is negative)
        qispos(q)               (number is positive)
        qisint(q)               (number is an integer)
        qisfrac(q)              (number is fractional)
        qisunit(q)              (number is 1 or -1)
        qisone(q)               (number is 1)
        qisnegone(q)            (number is -1)
        qistwo(q)               (number is 2)
        qiseven(q)              (number is an even integer)
        qisodd(q)               (number is an odd integer)
        qisreciprocal(q)        (number is 1 / an integer and q != 0)

The comparisons for NUMBERs are similar to the ones for ZVALUEs.  You use the
qcmp and qrel functions.

There are four predefined values for fractions.  You should qlink them when
you want to use them.  These are _qzero_, _qone_, _qnegone_, and _qonehalf_.
These have the values 0, 1, -1, and 1/2.  An example of using them is:

        NUMBER *q1, *q2;

        q1 = qlink(&_qonehalf_);
        q2 = qlink(&_qone_);

To determine if q is an integer power of 2, use qispowerof2:

        NUMBER *q;              /* value to check if it is a power of */
        NUMBER *qlog2;          /* set to log base 2 of q when is_power_of_2 is true */
        bool is_power_of_2;

        q = utoq((FULL) 1234567890L);
        qlog2 = qalloc();
        is_power_of_2 = qispowerof2(q, &qlog2);

Returns true if q an integer power of 2: set *qlog2 to log base 2 of q.
Returns false if q is NOT integer power of 2 and leave *qlog2 untouched.
Use qalloc() to setup the qlog2 arg before calling.

---------------------
USING COMPLEX NUMBERS
---------------------

The arbitrary precision complex arithmetic routines define a structure
called COMPLEX.  This is defined in cmath.h.  This contains two NUMBERs
for the real and imaginary parts of a complex number, and a count of the
number of links there are to this COMPLEX number.

The complex number routines work similarly to the fractional routines.
You can allocate a COMPLEX structure using comalloc (NOT calloc!).
You can construct a COMPLEX number with desired real and imaginary
fractional parts using qqtoc.  You can copy COMPLEX values using clink
which increments the link count.  And you free a COMPLEX value using cfree.
The following example illustrates this:

        NUMBER *q1, *q2;
        COMPLEX *c1, *c2, *c3;

        q1 = itoq(3L);
        q2 = itoq(4L);
        c1 = qqtoc(q1, q2);
        qfree(q1);
        qfree(q2);
        c2 = clink(c1);
        c3 = cmul(c1, c2);
        cfree(c1);
        cfree(c2);
        cfree(c3);

As a shortcut, when you want to manipulate a COMPLEX value by a real value,
you can use the caddq, csubq, cmulq, and cdivq routines.  These accept one
COMPLEX value and one NUMBER value, and produce a COMPLEX value.

There is no direct routine to convert a string value into a COMPLEX value.
But you can do this yourself by converting two strings into two NUMBERS,
and then using the qqtoc routine.

COMPLEX values are always returned from these routines.  To split out the
real and imaginary parts into normal NUMBERs, you can simply qlink the
two components, as shown in the following example:

        COMPLEX *c;
        NUMBER *rp, *ip;

        c = calloc();
        rp = qlink(c->real);
        ip = qlink(c->imag);

There are many macros for checking quick things about complex numbers,
similar to the ZVALUE and NUMBER macros.  In addition, there are some
only used for complex numbers.  Examples of macros are:

        cisreal(c)      (number is real)
        cisimag(c)      (number is pure imaginary)
        ciszero(c)      (number is zero)
        cisnegone(c)    (number is -1)
        cisone(c)       (number is 1)
        cisrunit(c)     (number is 1 or -1)
        cisiunit(c)     (number is i or -i)
        cisunit(c)      (number is 1, -1, i, or -i)
        cistwo(c)       (number is 2)
        cisint(c)       (number is has integer real and imaginary parts)
        ciseven(c)      (number is has even real and imaginary parts)
        cisodd(c)       (number is has odd real and imaginary parts)

There is only one comparison you can make for COMPLEX values, and that is
for equality.  The ccmp function returns true if two complex numbers differ.

Sometimes to results of a COMPLEX based calculation is a real number.
That is, the imaginary part of the COMPLEX is 0.  You may convert the
COMPLEX into a new allocated NUMBER that is real part of the COMPLEX value.
For example:

        COMPLEX *c;
        NUMBER *q;
        bool ok_to_free;        /* true ==> free COMPLEX value, false ==> do not */

        if (cisreal(c)) {
                q = c_to_q(c, ok_to_free);
        }

The 2nd argument to c_to_q() determines if the complex argument should be freed
or not.  Pass a false value as the 2nd arg if you wish to continue to use the
COMPLEX value.

To convert a NUMBER into a COMPLEX value, use:

        COMPLEX *c;
        NUMBER *q;

        c = q_to_c(q);

There are three predefined values for complex numbers.  You should clink
them when you want to use them.  They are _czero_, _cone_, and _conei_.
These have the values 0, 1, and i.

----------------
LAST THINGS LAST
----------------

If you wish, when you are all done you can call libcalc_call_me_last()
to free a small amount of storage associated with the libcalc_call_me_first()
call.  This is not required, but is does bring things to a closure.

The function libcalc_call_me_last() takes no args and returns void.  You
need call libcalc_call_me_last() only once.

## Copyright (C) 1999,2021,2023  David I. Bell and Landon Curt Noll
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License
## as published by the Free Software Foundation.
##
## Calc is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
## or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General
## Public License for more details.
##
## A copy of version 2.1 of the GNU Lesser General Public License is
## distributed with calc under the filename COPYING-LGPL.  You should have
## received a copy with calc; if not, write to Free Software Foundation, Inc.
## 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
##
## Under source code control:   1993/07/30 19:44:49
## File existed as early as:    1993
##
## chongo <was here> /\oo/\     http://www.isthe.com/chongo/
## Share and enjoy!  :-)        http://www.isthe.com/chongo/tech/comp/calc/
