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/*************************************************
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* libucp - Unicode Property Table handler *
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*************************************************/
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/* Internal header file defining the layout of compact nodes in the tree. */
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typedef struct cnode {
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unsigned short int f0;
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unsigned short int f1;
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unsigned short int f2;
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} cnode;
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/* Things for the f0 field */
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#define f0_leftexists 0x8000 /* Left child exists */
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#define f0_typemask 0x3f00 /* Type bits */
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#define f0_typeshift 8 /* Type shift */
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#define f0_chhmask 0x00ff /* Character high bits */
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/* Things for the f2 field */
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#define f2_rightmask 0xf000 /* Mask for right offset bits */
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#define f2_rightshift 12 /* Shift for right offset */
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#define f2_casemask 0x0fff /* Mask for case offset */
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/* The tree consists of a vector of structures of type cnode, with the root
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node as the first element. The three short ints (16-bits) are used as follows:
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(f0) (1) The 0x8000 bit of f0 is set if a left child exists. The child's node
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is the next node in the vector.
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(2) The 0x4000 bits of f0 is spare.
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(3) The 0x3f00 bits of f0 contain the character type; this is a number
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defined by the enumeration in ucp.h (e.g. ucp_Lu).
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(4) The bottom 8 bits of f0 contain the most significant byte of the
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character's 24-bit codepoint.
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(f1) (1) The f1 field contains the two least significant bytes of the
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codepoint.
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(f2) (1) The 0xf000 bits of f2 contain zero if there is no right child of this
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node. Otherwise, they contain one plus the exponent of the power of
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two of the offset to the right node (e.g. a value of 3 means 8). The
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units of the offset are node items.
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(2) The 0x0fff bits of f2 contain the signed offset from this character to
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its alternate cased value. They are zero if there is no such
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character.
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-----------------------------------------------------------------------------
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||.|.| type (6) | ms char (8) || ls char (16) ||....| case offset (12) ||
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-----------------------------------------------------------------------------
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| | |
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| |-> spare |
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| exponent of right
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|-> left child exists child offset
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The upper/lower casing information is set only for characters that come in
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pairs. There are (at present) four non-one-to-one mappings in the Unicode data.
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These are ignored. They are:
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1FBE Greek Prosgegrammeni (lower, with upper -> capital iota)
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2126 Ohm
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212A Kelvin
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212B Angstrom
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Certainly for the last three, having an alternate case would seem to be a
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mistake. I don't know any Greek, so cannot comment on the first one.
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When searching the tree, proceed as follows:
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(1) Start at the first node.
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(2) Extract the character value from f1 and the bottom 8 bits of f0;
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(3) Compare with the character being sought. If equal, we are done.
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(4) If the test character is smaller, inspect the f0_leftexists flag. If it is
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not set, the character is not in the tree. If it is set, move to the next
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node, and go to (2).
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(5) If the test character is bigger, extract the f2_rightmask bits from f2, and
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shift them right by f2_rightshift. If the result is zero, the character is
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not in the tree. Otherwise, calculate the number of nodes to skip by
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shifting the value 1 left by this number minus one. Go to (2).
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*/
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/* End of internal.h */
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