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Comment changes.
This commit is contained in:
Richard M. Stallman
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src/coding.c
116
src/coding.c
@ -44,41 +44,40 @@ Boston, MA 02111-1307, USA. */
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0. Emacs' internal format (emacs-mule)
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Emacs itself holds a multi-lingual character in a buffer and a string
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in a special format. Details are described in the section 2.
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in a special format. Details are described in section 2.
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1. ISO2022
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The most famous coding system for multiple character sets. X's
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Compound Text, various EUCs (Extended Unix Code), and such coding
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systems used in Internet communication as ISO-2022-JP are all
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variants of ISO2022. Details are described in the section 3.
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Compound Text, various EUCs (Extended Unix Code), and coding
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systems used in Internet communication such as ISO-2022-JP are
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all variants of ISO2022. Details are described in section 3.
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2. SJIS (or Shift-JIS or MS-Kanji-Code)
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A coding system to encode character sets: ASCII, JISX0201, and
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JISX0208. Widely used for PC's in Japan. Details are described in
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the section 4.
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section 4.
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3. BIG5
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A coding system to encode character sets: ASCII and Big5. Widely
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used by Chinese (mainly in Taiwan and Hong Kong). Details are
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described in the section 4. In this file, when written as "BIG5"
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(all uppercase), it means the coding system, and when written as
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"Big5" (capitalized), it means the character set.
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described in section 4. In this file, when we write "BIG5"
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(all uppercase), we mean the coding system, and when we write
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"Big5" (capitalized), we mean the character set.
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4. Else
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4. Other
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If a user want to read/write a text encoded in a coding system not
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If a user wants to read/write a text encoded in a coding system not
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listed above, he can supply a decoder and an encoder for it in CCL
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(Code Conversion Language) programs. Emacs executes the CCL program
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while reading/writing.
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Emacs represent a coding-system by a Lisp symbol that has a property
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Emacs represents a coding-system by a Lisp symbol that has a property
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`coding-system'. But, before actually using the coding-system, the
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information about it is set in a structure of type `struct
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coding_system' for rapid processing. See the section 6 for more
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detail.
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coding_system' for rapid processing. See section 6 for more details.
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*/
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@ -86,14 +85,13 @@ Boston, MA 02111-1307, USA. */
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How end-of-line of a text is encoded depends on a system. For
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instance, Unix's format is just one byte of `line-feed' code,
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whereas DOS's format is two bytes sequence of `carriage-return' and
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whereas DOS's format is two-byte sequence of `carriage-return' and
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`line-feed' codes. MacOS's format is one byte of `carriage-return'.
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Since how characters in a text is encoded and how end-of-line is
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encoded is independent, any coding system described above can take
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Since text characters encoding and end-of-line encoding are
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independent, any coding system described above can take
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any format of end-of-line. So, Emacs has information of format of
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end-of-line in each coding-system. See the section 6 for more
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detail.
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end-of-line in each coding-system. See section 6 for more details.
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*/
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@ -117,10 +115,10 @@ detect_coding_emacs_mule (src, src_end)
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These functions decode SRC_BYTES length text at SOURCE encoded in
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CODING to Emacs' internal format (emacs-mule). The resulting text
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goes to a place pointed by DESTINATION, the length of which should
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not exceed DST_BYTES. The bytes actually processed is returned as
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*CONSUMED. The return value is the length of the decoded text.
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Below is a template of these functions. */
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goes to a place pointed to by DESTINATION, the length of which should
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not exceed DST_BYTES. The number of bytes actually processed is
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returned as *CONSUMED. The return value is the length of the decoded
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text. Below is a template of these functions. */
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#if 0
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decode_coding_XXX (coding, source, destination, src_bytes, dst_bytes, consumed)
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struct coding_system *coding;
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@ -136,10 +134,10 @@ decode_coding_XXX (coding, source, destination, src_bytes, dst_bytes, consumed)
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These functions encode SRC_BYTES length text at SOURCE of Emacs'
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internal format (emacs-mule) to CODING. The resulting text goes to
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a place pointed by DESTINATION, the length of which should not
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exceed DST_BYTES. The bytes actually processed is returned as
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*CONSUMED. The return value is the length of the encoded text.
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Below is a template of these functions. */
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a place pointed to by DESTINATION, the length of which should not
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exceed DST_BYTES. The number of bytes actually processed is
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returned as *CONSUMED. The return value is the length of the
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encoded text. Below is a template of these functions. */
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#if 0
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encode_coding_XXX (coding, source, destination, src_bytes, dst_bytes, consumed)
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struct coding_system *coding;
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@ -200,7 +198,7 @@ encode_coding_XXX (coding, source, destination, src_bytes, dst_bytes, consumed)
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*dst++ = (c); \
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} while (0)
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/* Decode one DIMENSION1 character of which charset is CHARSET and
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/* Decode one DIMENSION1 character whose charset is CHARSET and whose
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position-code is C. */
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#define DECODE_CHARACTER_DIMENSION1(charset, c) \
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@ -215,7 +213,7 @@ encode_coding_XXX (coding, source, destination, src_bytes, dst_bytes, consumed)
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*dst++ = (c) | 0x80; \
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} while (0)
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/* Decode one DIMENSION2 character of which charset is CHARSET and
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/* Decode one DIMENSION2 character whose charset is CHARSET and whose
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position-codes are C1 and C2. */
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#define DECODE_CHARACTER_DIMENSION2(charset, c1, c2) \
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@ -337,25 +335,25 @@ Lisp_Object Vdefault_process_coding_system;
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/*** 2. Emacs internal format (emacs-mule) handlers ***/
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/* Emacs' internal format for encoding multiple character sets is a
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kind of multi-byte encoding, i.e. encoding a character by a sequence
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of one-byte codes of variable length. ASCII characters and control
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characters (e.g. `tab', `newline') are represented by one-byte as
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is. It takes the range 0x00 through 0x7F. The other characters
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are represented by a sequence of `base leading-code', optional
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`extended leading-code', and one or two `position-code's. Length
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of the sequence is decided by the base leading-code. Leading-code
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takes the range 0x80 through 0x9F, whereas extended leading-code
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and position-code take the range 0xA0 through 0xFF. See the
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document of `charset.h' for more detail about leading-code and
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position-code.
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kind of multi-byte encoding, i.e. characters are encoded by
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variable-length sequences of one-byte codes. ASCII characters
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and control characters (e.g. `tab', `newline') are represented by
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one-byte sequences which are their ASCII codes, in the range 0x00
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through 0x7F. The other characters are represented by a sequence
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of `base leading-code', optional `extended leading-code', and one
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or two `position-code's. The length of the sequence is determined
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by the base leading-code. Leading-code takes the range 0x80
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through 0x9F, whereas extended leading-code and position-code take
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the range 0xA0 through 0xFF. See `charset.h' for more details
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about leading-code and position-code.
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There's one exception in this rule. Special leading-code
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There's one exception to this rule. Special leading-code
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`leading-code-composition' denotes that the following several
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characters should be composed into one character. Leading-codes of
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components (except for ASCII) are added 0x20. An ASCII character
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component is represented by a 2-byte sequence of `0xA0' and
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`ASCII-code + 0x80'. See also the document in `charset.h' for the
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detail of composite character. Hence, we can summarize the code
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`ASCII-code + 0x80'. See also the comments in `charset.h' for the
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details of composite character. Hence, we can summarize the code
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range as follows:
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--- CODE RANGE of Emacs' internal format ---
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@ -447,21 +445,21 @@ detect_coding_emacs_mule (src, src_end)
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/*** 3. ISO2022 handlers ***/
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/* The following note describes the coding system ISO2022 briefly.
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Since the intension of this note is to help understanding of the
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programs in this file, some parts are NOT ACCURATE or OVERLY
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Since the intention of this note is to help in understanding of
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the programs in this file, some parts are NOT ACCURATE or OVERLY
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SIMPLIFIED. For the thorough understanding, please refer to the
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original document of ISO2022.
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ISO2022 provides many mechanisms to encode several character sets
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in 7-bit and 8-bit environment. If one choose 7-bite environment,
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in 7-bit and 8-bit environment. If one chooses 7-bite environment,
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all text is encoded by codes of less than 128. This may make the
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encoded text a little bit longer, but the text get more stability
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to pass through several gateways (some of them split MSB off).
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encoded text a little bit longer, but the text gets more stability
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to pass through several gateways (some of them strip off the MSB).
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There are two kind of character set: control character set and
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There are two kinds of character set: control character set and
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graphic character set. The former contains control characters such
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as `newline' and `escape' to provide control functions (control
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functions are provided also by escape sequence). The latter
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functions are provided also by escape sequences). The latter
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contains graphic characters such as ' A' and '-'. Emacs recognizes
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two control character sets and many graphic character sets.
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@ -565,7 +563,7 @@ detect_coding_emacs_mule (src, src_end)
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'(' can be omitted. We call this as "short-form" here after.
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Now you may notice that there are a lot of ways for encoding the
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same multilingual text in ISO2022. Actually, there exist many
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same multilingual text in ISO2022. Actually, there exists many
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coding systems such as Compound Text (used in X's inter client
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communication, ISO-2022-JP (used in Japanese Internet), ISO-2022-KR
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(used in Korean Internet), EUC (Extended UNIX Code, used in Asian
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@ -1018,10 +1016,10 @@ decode_coding_iso2022 (coding, source, destination,
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return dst - destination;
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}
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/* ISO2022 encoding staffs. */
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/* ISO2022 encoding stuff. */
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/*
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It is not enough to say just "ISO2022" on encoding, but we have to
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It is not enough to say just "ISO2022" on encoding, we have to
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specify more details. In Emacs, each coding-system of ISO2022
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variant has the following specifications:
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1. Initial designation to G0 thru G3.
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@ -1036,7 +1034,7 @@ decode_coding_iso2022 (coding, source, destination,
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9. Use JISX0208-1983 in place of JISX0208-1978?
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These specifications are encoded in `coding->flags' as flag bits
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defined by macros CODING_FLAG_ISO_XXX. See `coding.h' for more
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detail.
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details.
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*/
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/* Produce codes (escape sequence) for designating CHARSET to graphic
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@ -1132,8 +1130,8 @@ decode_coding_iso2022 (coding, source, destination,
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CODING_SPEC_ISO_INVOCATION (coding, 0) = 3; \
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} while (0)
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/* Produce codes for a DIMENSION1 character of which character set is
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CHARSET and position-code is C1. Designation and invocation
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/* Produce codes for a DIMENSION1 character whose character set is
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CHARSET and whose position-code is C1. Designation and invocation
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sequences are also produced in advance if necessary. */
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@ -1166,8 +1164,8 @@ decode_coding_iso2022 (coding, source, destination,
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dst = encode_invocation_designation (charset, coding, dst); \
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} while (1)
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/* Produce codes for a DIMENSION2 character of which character set is
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CHARSET and position-codes are C1 and C2. Designation and
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/* Produce codes for a DIMENSION2 character whose character set is
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CHARSET and whose position-codes are C1 and C2. Designation and
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invocation codes are also produced in advance if necessary. */
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#define ENCODE_ISO_CHARACTER_DIMENSION2(charset, c1, c2) \
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@ -1552,7 +1550,7 @@ encode_coding_iso2022 (coding, source, destination,
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/*** 4. SJIS and BIG5 handlers ***/
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/* Although SJIS and BIG5 are not ISO's coding system, They are used
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/* Although SJIS and BIG5 are not ISO's coding system, they are used
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quite widely. So, for the moment, Emacs supports them in the bare
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C code. But, in the future, they may be supported only by CCL. */
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@ -2167,7 +2165,7 @@ setup_coding_system (coding_system, coding)
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{
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Lisp_Object type, eol_type;
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/* At first, set several fields default values. */
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/* At first, set several fields to default values. */
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coding->require_flushing = 0;
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coding->last_block = 0;
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coding->selective = 0;
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