char.c

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/*-------------------------------------------------------------------------
 *
 * char.c
 *    Functions for the built-in type "char" (not to be confused with
 *    bpchar, which is the SQL CHAR(n) type).
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/char.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <limits.h>

#include "libpq/pqformat.h"
#include "utils/builtins.h"

/*****************************************************************************
 *   USER I/O ROUTINES                                                       *
 *****************************************************************************/

/*
 *      charin          - converts "x" to 'x'
 *
 * Note that an empty input string will implicitly be converted to \0.
 */
Datum
charin(PG_FUNCTION_ARGS)
{
    char       *ch = PG_GETARG_CSTRING(0);

    PG_RETURN_CHAR(ch[0]);
}

/*
 *      charout         - converts 'x' to "x"
 *
 * Note that if the char value is \0, the resulting string will appear
 * to be empty (null-terminated after zero characters).  So this is the
 * inverse of the charin() function for such data.
 */
Datum
charout(PG_FUNCTION_ARGS)
{
    char        ch = PG_GETARG_CHAR(0);
    char       *result = (char *) palloc(2);

    result[0] = ch;
    result[1] = '\0';
    PG_RETURN_CSTRING(result);
}

/*
 *      charrecv            - converts external binary format to char
 *
 * The external representation is one byte, with no character set
 * conversion.  This is somewhat dubious, perhaps, but in many
 * cases people use char for a 1-byte binary type.
 */
Datum
charrecv(PG_FUNCTION_ARGS)
{
    StringInfo  buf = (StringInfo) PG_GETARG_POINTER(0);

    PG_RETURN_CHAR(pq_getmsgbyte(buf));
}

/*
 *      charsend            - converts char to binary format
 */
Datum
charsend(PG_FUNCTION_ARGS)
{
    char        arg1 = PG_GETARG_CHAR(0);
    StringInfoData buf;

    pq_begintypsend(&buf);
    pq_sendbyte(&buf, arg1);
    PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
}

/*****************************************************************************
 *   PUBLIC ROUTINES                                                         *
 *****************************************************************************/

/*
 * NOTE: comparisons are done as though char is unsigned (uint8).
 * Conversions to and from integer are done as though char is signed (int8).
 *
 * You wanted consistency?
 */

Datum
chareq(PG_FUNCTION_ARGS)
{
    char        arg1 = PG_GETARG_CHAR(0);
    char        arg2 = PG_GETARG_CHAR(1);

    PG_RETURN_BOOL(arg1 == arg2);
}

Datum
charne(PG_FUNCTION_ARGS)
{
    char        arg1 = PG_GETARG_CHAR(0);
    char        arg2 = PG_GETARG_CHAR(1);

    PG_RETURN_BOOL(arg1 != arg2);
}

Datum
charlt(PG_FUNCTION_ARGS)
{
    char        arg1 = PG_GETARG_CHAR(0);
    char        arg2 = PG_GETARG_CHAR(1);

    PG_RETURN_BOOL((uint8) arg1 < (uint8) arg2);
}

Datum
charle(PG_FUNCTION_ARGS)
{
    char        arg1 = PG_GETARG_CHAR(0);
    char        arg2 = PG_GETARG_CHAR(1);

    PG_RETURN_BOOL((uint8) arg1 <= (uint8) arg2);
}

Datum
chargt(PG_FUNCTION_ARGS)
{
    char        arg1 = PG_GETARG_CHAR(0);
    char        arg2 = PG_GETARG_CHAR(1);

    PG_RETURN_BOOL((uint8) arg1 > (uint8) arg2);
}

Datum
charge(PG_FUNCTION_ARGS)
{
    char        arg1 = PG_GETARG_CHAR(0);
    char        arg2 = PG_GETARG_CHAR(1);

    PG_RETURN_BOOL((uint8) arg1 >= (uint8) arg2);
}


Datum
chartoi4(PG_FUNCTION_ARGS)
{
    char        arg1 = PG_GETARG_CHAR(0);

    PG_RETURN_INT32((int32) ((int8) arg1));
}

Datum
i4tochar(PG_FUNCTION_ARGS)
{
    int32       arg1 = PG_GETARG_INT32(0);

    if (arg1 < SCHAR_MIN || arg1 > SCHAR_MAX)
        ereport(ERROR,
                (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                 errmsg("\"char\" out of range")));

    PG_RETURN_CHAR((int8) arg1);
}


Datum
text_char(PG_FUNCTION_ARGS)
{
    text       *arg1 = PG_GETARG_TEXT_PP(0);
    char        result;

    /*
     * An empty input string is converted to \0 (for consistency with charin).
     * If the input is longer than one character, the excess data is silently
     * discarded.
     */
    if (VARSIZE_ANY_EXHDR(arg1) > 0)
        result = *(VARDATA_ANY(arg1));
    else
        result = '\0';

    PG_RETURN_CHAR(result);
}

Datum
char_text(PG_FUNCTION_ARGS)
{
    char        arg1 = PG_GETARG_CHAR(0);
    text       *result = palloc(VARHDRSZ + 1);

    /*
     * Convert \0 to an empty string, for consistency with charout (and
     * because the text stuff doesn't like embedded nulls all that well).
     */
    if (arg1 != '\0')
    {
        SET_VARSIZE(result, VARHDRSZ + 1);
        *(VARDATA(result)) = arg1;
    }
    else
        SET_VARSIZE(result, VARHDRSZ);

    PG_RETURN_TEXT_P(result);
}