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Date: Sun, 20 Nov 2011 00:54:15 +0900
From: NamJae Jeon <linkinjeon@...il.com>
To: Alan Stern <stern@...land.harvard.edu>
Cc: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
Greg KH <greg@...ah.com>, Clemens Ladisch <clemens@...isch.de>,
USB list <linux-usb@...r.kernel.org>,
Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] NLS: improve UTF8 -> UTF16 string conversion routine
2011/11/20 NamJae Jeon <linkinjeon@...il.com>:
> 2011/11/20 Alan Stern <stern@...land.harvard.edu>:
>> On Sat, 19 Nov 2011, NamJae Jeon wrote:
>>
>>> >> > +int utf8s_to_utf16s(const u8 *s, int len, enum utf16_endian endian,
>>> >> > + wchar_t *pwcs, int maxlen)
>>> >> > {
>>> >> > u16 *op;
>>> >> > int size;
>>> >> > unicode_t u;
>>> >> >
>>> >> > op = pwcs;
>>> >> > - while (*s && len > 0) {
>>> >> > + while (len > 0 && maxlen > 0 && *s) {
>>> >> > if (*s & 0x80) {
>>> >> > size = utf8_to_utf32(s, len, &u);
>>> >> > if (size < 0)
>>> >> > return -EINVAL;
>>> >> > + s += size;
>>> >> > + len -= size;
>> ...
>>> >> > if (u >= PLANE_SIZE) {
>>> >> > + if (maxlen < 2)
>>> >> > + break;
>>> >> > u -= PLANE_SIZE;
>>> >> > - *op++ = (wchar_t) (SURROGATE_PAIR |
>>> >> > - ((u >> 10) & SURROGATE_BITS));
>>> >> > - *op++ = (wchar_t) (SURROGATE_PAIR |
>>> >> > + put_utf16(op++, SURROGATE_PAIR |
>>> >> > + ((u >> 10) & SURROGATE_BITS),
>>> >> > + endian);
>>> >> > + put_utf16(op++, SURROGATE_PAIR |
>>> >> > SURROGATE_LOW |
>>> >> > - (u & SURROGATE_BITS));
>>> >> > + (u & SURROGATE_BITS),
>>> >> > + endian);
>>> >> > + maxlen -= 2;
>>> >>
>>> >> Why did you use contants value(-2) instead of maxlen -= size; value ?
>>> >
>>> > "maxlen -= size" would be completely wrong, because size is the length
>>> > of the utf8 input and maxlen is the number of 16-bit slots remaining
>>> > in the output buffer. A surrogate pair uses two 16-bit values,
>>> > therefore maxlen has to be decreased by 2.
>>> If so, len should also be minus -2 constant value like maxlen ?
>>
>> You seem to be confused. "len" refers to the input string and "maxlen"
>> refers to the output string. They have no connection to one another.
>> Would it help if "maxlen" were named "maxout" instead?
> okay, I knew clearly. If you will, I'm grateful.
> I suggest code is a little changed about maxout. how do you think ?
> --------------------------------------------------------------------------------------------------------------
> + s += size;
> + len -= size;
> + maxout--
>
> if (u >= PLANE_SIZE) {
> + if (maxlen < 2)
> + break;
> u -= PLANE_SIZE;
> - *op++ = (wchar_t) (SURROGATE_PAIR |
> - ((u >> 10) & SURROGATE_BITS));
> - *op++ = (wchar_t) (SURROGATE_PAIR |
> + put_utf16(op++, SURROGATE_PAIR |
> + ((u >> 10) & SURROGATE_BITS),
> + endian);
> + put_utf16(op++, SURROGATE_PAIR |
> SURROGATE_LOW |
> - (u & SURROGATE_BITS));
> + (u & SURROGATE_BITS),
> + endian);
> + maxout--;
sorry,, I changed maxout.
> } else {
> - *op++ = (wchar_t) u;
> + put_utf16(op++, u, endian);
> }
>
> -----------------------------------------------------------------------------------------------------------------------------------------
>
>>
>>> and why does this code(if (maxlen < 2)) is needed ? If len is smaller than 2 ?
>>
>> If maxlen < 2 then there is room in the output buffer for only one more
>> data value -- but a surrogate pair occupies two data values. Hence
>> there isn't room to store the pair in the output buffer, so the loop
>> must terminate.
>>
>>> >> > } else {
>>> >> > - *op++ = (wchar_t) u;
>>> >> > + put_utf16(op++, u, endian);
>>> >> > + maxlen--;
>>> >> > }
>>> >> > - s += size;
>>> >> > - len -= size;
>>> >> > } else {
>>> >> > - *op++ = *s++;
>>> >> > + put_utf16(op++, *s++, endian);
>>> >> > len--;
>>> >> > + maxlen--;
>>> >> > }
>>> >> > }
>>> >> > return op - pwcs;
>>> >> > Index: usb-3.2/fs/fat/namei_vfat.c
>>> >> > ===================================================================
>>> >> > --- usb-3.2.orig/fs/fat/namei_vfat.c
>>> >> > +++ usb-3.2/fs/fat/namei_vfat.c
>>> >> > @@ -512,7 +512,8 @@ xlate_to_uni(const unsigned char *name,
>>> >> > int charlen;
>>> >> >
>>> >> > if (utf8) {
>>> >> > - *outlen = utf8s_to_utf16s(name, len, (wchar_t *)outname);
>>> >> > + *outlen = utf8s_to_utf16s(name, len, UTF16_HOST_ENDIAN,
>>> >> > + (wchar_t *) outname, FAT_LFN_LEN + 2);
>>> >> Is there the reason why you plus 2 to FAT_LFN_LEN ?
>>> >
>>> > So that the "(*outlen > FAT_LFN_LEN)" test below will work correctly.
>>> > If the maximum length were set to FAT_LFN_LEN then the test would
>>> > always fail. If the maximum length were set to FAT_LFN_LEN + 1 then
>>> > the test would fail when the next character to be stored was a
>>> > surrogate pair.
>>> Although we are using maxlen, I don't know why do we check case that
>>> outlen is bigger than FAT_LFN_LEN.
>>
>> Probably because the filesystem code requires that the UTF16 string fit
>> into a certain amount of space. If *outlen > FAT_LFN_LEN then the
>> string doesn't fit.
>>
>> Alan Stern
>>
>>
>
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