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) 1996-2025, 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/fmgrprotos.h"
#include "varatt.h"
 
#define ISOCTAL(c)   (((c) >= '0') && ((c) <= '7'))
#define TOOCTAL(c)   ((c) + '0')
#define FROMOCTAL(c) ((unsigned char) (c) - '0')
 
 
/*****************************************************************************
 *   USER I/O ROUTINES                                                       *
 *****************************************************************************/
 
/*
 *      charin          - converts "x" to 'x'
 *
 * This accepts the formats charout produces.  If we have multibyte input
 * that is not in the form '\ooo', then we take its first byte as the value
 * and silently discard the rest; this is a backwards-compatibility provision.
 */
Datum
charin(PG_FUNCTION_ARGS)
{
    char       *ch = PG_GETARG_CSTRING(0);
 
    if (strlen(ch) == 4 && ch[0] == '\\' &&
        ISOCTAL(ch[1]) && ISOCTAL(ch[2]) && ISOCTAL(ch[3]))
        PG_RETURN_CHAR((FROMOCTAL(ch[1]) << 6) +
                       (FROMOCTAL(ch[2]) << 3) +
                       FROMOCTAL(ch[3]));
    /* This will do the right thing for a zero-length input string */
    PG_RETURN_CHAR(ch[0]);
}
 
/*
 *      charout         - converts 'x' to "x"
 *
 * The possible output formats are:
 * 1. 0x00 is represented as an empty string.
 * 2. 0x01..0x7F are represented as a single ASCII byte.
 * 3. 0x80..0xFF are represented as \ooo (backslash and 3 octal digits).
 * Case 3 is meant to match the traditional "escape" format of bytea.
 */
Datum
charout(PG_FUNCTION_ARGS)
{
    char        ch = PG_GETARG_CHAR(0);
    char       *result = (char *) palloc(5);
 
    if (IS_HIGHBIT_SET(ch))
    {
        result[0] = '\\';
        result[1] = TOOCTAL(((unsigned char) ch) >> 6);
        result[2] = TOOCTAL((((unsigned char) ch) >> 3) & 07);
        result[3] = TOOCTAL(((unsigned char) ch) & 07);
        result[4] = '\0';
    }
    else
    {
        /* This produces acceptable results for 0x00 as well */
        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       *ch = VARDATA_ANY(arg1);
    char        result;
 
    /*
     * Conversion rules are the same as in charin(), but here we need to
     * handle the empty-string case honestly.
     */
    if (VARSIZE_ANY_EXHDR(arg1) == 4 && ch[0] == '\\' &&
        ISOCTAL(ch[1]) && ISOCTAL(ch[2]) && ISOCTAL(ch[3]))
        result = (FROMOCTAL(ch[1]) << 6) +
            (FROMOCTAL(ch[2]) << 3) +
            FROMOCTAL(ch[3]);
    else if (VARSIZE_ANY_EXHDR(arg1) > 0)
        result = ch[0];
    else
        result = '\0';
 
    PG_RETURN_CHAR(result);
}
 
Datum
char_text(PG_FUNCTION_ARGS)
{
    char        arg1 = PG_GETARG_CHAR(0);
    text       *result = palloc(VARHDRSZ + 4);
 
    /*
     * Conversion rules are the same as in charout(), but here we need to be
     * honest about converting 0x00 to an empty string.
     */
    if (IS_HIGHBIT_SET(arg1))
    {
        SET_VARSIZE(result, VARHDRSZ + 4);
        (VARDATA(result))[0] = '\\';
        (VARDATA(result))[1] = TOOCTAL(((unsigned char) arg1) >> 6);
        (VARDATA(result))[2] = TOOCTAL((((unsigned char) arg1) >> 3) & 07);
        (VARDATA(result))[3] = TOOCTAL(((unsigned char) arg1) & 07);
    }
    else if (arg1 != '\0')
    {
        SET_VARSIZE(result, VARHDRSZ + 1);
        *(VARDATA(result)) = arg1;
    }
    else
        SET_VARSIZE(result, VARHDRSZ);
 
    PG_RETURN_TEXT_P(result);
}