for (i=0 ; i<2 ; i++) {
	    if (data >= dataend) {
		value <<= 4;
		break;
	    }

	    c = *data++;
	    if (!isxdigit(UCHAR(c))) {
		if (strict || !TclIsSpaceProc(c)) {
		    goto badChar;
		}
		i--;
		continue;
	    }

	    value <<= 4;

    while (data < dataend) {
	char d[4] = {0, 0, 0, 0};

	if (lineLen < 0) {
	    c = *data++;
	    if (c < 32 || c > 96) {
		if (strict || !TclIsSpaceProc(c)) {
		    goto badUu;
		}
		i--;
		continue;
	    }
	    lineLen = (c - 32) & 0x3f;
	}

	/*
	 * Now we read a four-character grouping.
	 */

	for (i=0 ; i<4 ; i++) {
	    if (data < dataend) {
		d[i] = c = *data++;
		if (c < 32 || c > 96) {
		    if (strict) {
			if (!TclIsSpaceProc(c)) {
			    goto badUu;
			} else if (c == '\n') {
			    goto shortUu;
			}
		    }
		    i--;
		    continue;

	    do {
		c = *data++;
		if (c == '\n') {
		    break;
		} else if (c >= 32 && c <= 96) {
		    data--;
		    break;
		} else if (strict || !TclIsSpaceProc(c)) {
		    goto badUu;
		}
	    } while (data < dataend);
	}
    }

    /*

	     * input whitespace characters.
	     */

	    if (cut) {
		if (c == '=' && i > 1) {
		     value <<= 6;
		     cut++;
		} else if (!strict && TclIsSpaceProc(c)) {
		     i--;
		} else {
		    goto bad64;
		}
	    } else if (c >= 'A' && c <= 'Z') {
		value = (value << 6) | ((c - 'A') & 0x3f);
	    } else if (c >= 'a' && c <= 'z') {
		value = (value << 6) | ((c - 'a' + 26) & 0x3f);
	    } else if (c >= '0' && c <= '9') {
		value = (value << 6) | ((c - '0' + 52) & 0x3f);
	    } else if (c == '+') {
		value = (value << 6) | 0x3e;
	    } else if (c == '/') {
		value = (value << 6) | 0x3f;
	    } else if (c == '=') {
		value <<= 6;
		cut++;
	    } else if (strict || !TclIsSpaceProc(c)) {
		goto bad64;
	    } else {
		i--;
	    }
	}
	*cursor++ = UCHAR((value >> 16) & 0xff);
	*cursor++ = UCHAR((value >> 8) & 0xff);
	*cursor++ = UCHAR(value & 0xff);

	/*
	 * Since = is only valid within the final block, if it was encountered
	 * but there are still more input characters, confirm that strict mode
	 * is off and all subsequent characters are whitespace.
	 */

	if (cut && data < dataend) {
	    if (strict) {
		goto bad64;
	    }
	    for (; data < dataend; data++) {
		if (!TclIsSpaceProc(*data)) {
		    goto bad64;
		}
	    }
	}
    }
    Tcl_SetByteArrayLength(resultObj, cursor - begin - cut);
    Tcl_SetObjResult(interp, resultObj);