and Mac codepages reflect the character set from the Thai standard
TIS 620-2533. The character code on both platforms for the Thai
letter "SO SO" is 0xAB. This character can then be mapped into the
UCS-4 by way of a conversion/mapping file to produce the UCS-4 code
of 0x0E0B.
The UCS-4 character code is transformed into UTF-8 using the
ucs4_to_utf8 routine described earlier by:
1. Because the UCS-4 character is between 0x0800 and 0xFFFF it will
map to a 3 byte UTF-8 sequence.
2. The first byte is defined by (0xE0 + (0x00000E0B / 0x1000) = 0xE0.
3. The second byte is defined by (0x80 + ((0x00000E0B / 0x40) %
0x40))) = 0xB8.
4. The third byte is defined by (0x80 + (0x00000E0B % 0x40)) = 0x8B.
The UTF-8 encoding is transferred back to UCS-4 by using the
utf8_to_ucs4 routine described earlier by:
1. Because the first byte of the sequence, when the '&' operator with
a value of 0xF0 is applied, will produce 0xE0 (0xE0 & 0xF0 = 0xE0)
the UTF-8 is a 3 byte sequence.
2. The four byte UCS-4 character code is produced by (((0xE0 - 0xE0)
* 0x1000) + ((0xB8 - 0x80) * 0x40) + (0x8B -0x80) = 0x0000E0B.
Finally, the UCS-4 character code is converted to either the PC or
MAC codepage character code (using the mapping table which matches
codepage to UCS-4 ) to produce the original 0xAB code for the Thai
letter "SO SO".
B.3 Pseudo Code for a High-Quality Translating Server
if utf8_valid(fn)
{
attempt to convert fn to the local charset, producing localfn
if (conversion fails temporarily) return error
if (conversion succeeds)
{
attempt to open localfn
if (open fails temporarily) return error
if (open succeeds) return success
}
}
attempt to open fn
if (open fails temporarily) return error
if (open succeeds) return success
return permanent error
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