unsigned char *dst = byteArrayPtr->bytes;
    unsigned char *dstEnd = dst + numBytes;
    const char *srcEnd = src + length;
    int proper = 1;

    for (; src < srcEnd && dst < dstEnd; ) {
	int ch;
	int count = Tcl_UtfToUniChar(src, &ch);

	if (ch > 255) {
	    proper = 0;
	    if (demandProper) {
		if (interp) {
		    Tcl_SetObjResult(interp, Tcl_ObjPrintf(
			    "expected byte sequence but character %"

    Tcl_SetObjResult(interp, resultObj);
    return TCL_OK;

  badChar:
    if (pure) {
	ucs4 = c;
    } else {
	Tcl_UtfToUniChar((const char *)(data - 1), &ucs4);
    }
    TclDecrRefCount(resultObj);
    Tcl_SetObjResult(interp, Tcl_ObjPrintf(
	    "invalid hexadecimal digit \"%c\" (U+%06X) at position %"
	    TCL_Z_MODIFIER "u", ucs4, ucs4, data - datastart - 1));
    Tcl_SetErrorCode(interp, "TCL", "BINARY", "DECODE", "INVALID", NULL);
    return TCL_ERROR;

    TclDecrRefCount(resultObj);
    return TCL_ERROR;

  badUu:
    if (pure) {
	ucs4 = c;
    } else {
	Tcl_UtfToUniChar((const char *)(data - 1), &ucs4);
    }
    Tcl_SetObjResult(interp, Tcl_ObjPrintf(
	    "invalid uuencode character \"%c\" (U+%06X) at position %"
	    TCL_Z_MODIFIER "u", ucs4, ucs4, data - datastart - 1));
    Tcl_SetErrorCode(interp, "TCL", "BINARY", "DECODE", "INVALID", NULL);
    TclDecrRefCount(resultObj);
    return TCL_ERROR;

	ucs4 = c;
    } else {
	/* The decoder is byte-oriented. If we saw a byte that's not a
	 * valid member of the base64 alphabet, it could be the lead byte
	 * of a multi-byte character. */

	/* Safe because we know data is NUL-terminated */
	Tcl_UtfToUniChar((const char *)(data - 1), &ucs4);
    }

    Tcl_SetObjResult(interp, Tcl_ObjPrintf(
	    "invalid base64 character \"%c\" (U+%06X) at position %"
	    TCL_Z_MODIFIER "u", ucs4, ucs4, data - datastart - 1));
    Tcl_SetErrorCode(interp, "TCL", "BINARY", "DECODE", "INVALID", NULL);
    TclDecrRefCount(resultObj);