.TH "RQ Query" 3 2022-07-07 "LCRQ" "Librecast Programmer's Manual"
.SH NAME
rq_query - RaptorQ Query Functions
.SH SYNOPSIS
.nf
.B #include <lcrq.h>
.PP
.BI "uint8_t rq_Al(const rq_t * const " rq ");"
.BI "uint64_t rq_F(const rq_t * const " rq ");"
.BI "uint16_t rq_K(const rq_t * const " rq ");"
.BI "uint16_t rq_KP(const rq_t * const " rq ");"
.BI "uint16_t rq_T(const rq_t * const " rq ");"
.BI "uint16_t rq_N(const rq_t * const " rq ");"
.BI "uint8_t rq_Z(const rq_t * const " rq ");"
.fi
.PP
Compile and link with \fI\-llcrq\fP.
.SH DESCRIPTION
The RaptorQ query functions return the value of their respective RaptorQ parameters.
.PP
.B F
Transfer Length (F): 40-bit unsigned integer.  A non-negative
integer that is at most 946270874880.  This is the transfer length
of the object in units of octets.
.PP
.B T
Symbol Size (T): 16-bit unsigned integer.  A positive integer that
is less than 2^^16.  This is the size of a symbol in units of
octets. This MUST be a multiple of Al.
.PP
.B Al
A symbol alignment parameter (Al): 8-bit unsigned integer.
.PP
.B Z
The number of source blocks (Z): 16-bit unsigned integer.
.PP
.B K
The number of source symbols.
.PP
.B KP (K')
The number of source and padding symbols.
.PP
The parameter
.I rq
must be a pointer to RaptorQ context initialized with
.I rq_init\fP(3)
.PP
.SH RETURN VALUE
These functions return the RQ parameters as unsigned integers.
.SH ERRORS
These functions do not return errors.
.SH EXAMPLE
.SS Program source
\&
.EX
/* params - example program to create RaptorQ context and print derived parameters */

#include <lcrq.h>
#include <stdio.h>
#include <stdlib.h>

int usage(const char *progname)
{
        fprintf(stderr, "usage: `%s F T`  (F = object size, T = symbol size)\n", progname);
}

int main(int argc, char *argv[])
{
        rq_t *rq;
        uint64_t F;
        uint16_t T, K, KP, N, Z;
        uint8_t Al;

        if (argc != 3) return usage(argv[0]);
        F = atoll(argv[1]);
        T = atoll(argv[2]);

        /* initialize RaptorQ context */
        rq = rq_init(F, T);

        /* Query parameters */
        K = rq_K(rq);
        KP = rq_KP(rq);
        N = rq_N(rq);
        Z = rq_Z(rq);

        /* free RaptorQ context */
        rq_free(rq);

        printf("F  %12lu\tsize of object to encode (40 bits)\n", F);
        printf("T  %12u\tsymbol (payload) size\n", T);
        printf("K  %12u\tnumber of original symbols\n", K);
        printf("K' %12u\tnumber of symbols, including padding symbols\n", KP);
        printf("N  %12u\tnumber of sub-blocks\n", N);
        printf("Z  %12u\tnumber of blocks\n", Z);

        return 0;
}

rq_free(rq); /* free context when done */
.EE
.SH SEE ALSO
.BR rq_init (3),
.BR rq_free (3),
.BR rq_decode (3),
.BR rq_encode (3),
.BR rq_symbol (3),
.BR lcrq (7)