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135 lines
3.7 KiB
C
135 lines
3.7 KiB
C
/* Finding the optimal width of unicode characters in a buffer */
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#if !STRINGLIB_IS_UNICODE
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# error "find_max_char.h is specific to Unicode"
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#endif
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/* Mask to quickly check whether a C 'long' contains a
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non-ASCII, UTF8-encoded char. */
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#if (SIZEOF_LONG == 8)
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# define UCS1_ASCII_CHAR_MASK 0x8080808080808080UL
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#elif (SIZEOF_LONG == 4)
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# define UCS1_ASCII_CHAR_MASK 0x80808080UL
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#else
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# error C 'long' size should be either 4 or 8!
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#endif
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#if STRINGLIB_SIZEOF_CHAR == 1
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Py_LOCAL_INLINE(Py_UCS4)
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STRINGLIB(find_max_char)(const STRINGLIB_CHAR *begin, const STRINGLIB_CHAR *end)
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{
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const unsigned char *p = (const unsigned char *) begin;
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const unsigned char *aligned_end =
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(const unsigned char *) _Py_ALIGN_DOWN(end, SIZEOF_LONG);
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while (p < end) {
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if (_Py_IS_ALIGNED(p, SIZEOF_LONG)) {
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/* Help register allocation */
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const unsigned char *_p = p;
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while (_p < aligned_end) {
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unsigned long value = *(unsigned long *) _p;
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if (value & UCS1_ASCII_CHAR_MASK)
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return 255;
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_p += SIZEOF_LONG;
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}
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p = _p;
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if (p == end)
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break;
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}
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if (*p++ & 0x80)
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return 255;
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}
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return 127;
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}
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#undef ASCII_CHAR_MASK
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#else /* STRINGLIB_SIZEOF_CHAR == 1 */
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#define MASK_ASCII 0xFFFFFF80
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#define MASK_UCS1 0xFFFFFF00
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#define MASK_UCS2 0xFFFF0000
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#define MAX_CHAR_ASCII 0x7f
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#define MAX_CHAR_UCS1 0xff
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#define MAX_CHAR_UCS2 0xffff
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#define MAX_CHAR_UCS4 0x10ffff
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Py_LOCAL_INLINE(Py_UCS4)
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STRINGLIB(find_max_char)(const STRINGLIB_CHAR *begin, const STRINGLIB_CHAR *end)
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{
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#if STRINGLIB_SIZEOF_CHAR == 2
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const Py_UCS4 mask_limit = MASK_UCS1;
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const Py_UCS4 max_char_limit = MAX_CHAR_UCS2;
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#elif STRINGLIB_SIZEOF_CHAR == 4
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const Py_UCS4 mask_limit = MASK_UCS2;
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const Py_UCS4 max_char_limit = MAX_CHAR_UCS4;
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#else
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#error Invalid STRINGLIB_SIZEOF_CHAR (must be 1, 2 or 4)
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#endif
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Py_UCS4 mask;
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Py_ssize_t n = end - begin;
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const STRINGLIB_CHAR *p = begin;
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const STRINGLIB_CHAR *unrolled_end = begin + _Py_SIZE_ROUND_DOWN(n, 4);
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Py_UCS4 max_char;
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max_char = MAX_CHAR_ASCII;
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mask = MASK_ASCII;
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while (p < unrolled_end) {
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STRINGLIB_CHAR bits = p[0] | p[1] | p[2] | p[3];
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if (bits & mask) {
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if (mask == mask_limit) {
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/* Limit reached */
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return max_char_limit;
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}
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if (mask == MASK_ASCII) {
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max_char = MAX_CHAR_UCS1;
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mask = MASK_UCS1;
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}
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else {
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/* mask can't be MASK_UCS2 because of mask_limit above */
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assert(mask == MASK_UCS1);
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max_char = MAX_CHAR_UCS2;
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mask = MASK_UCS2;
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}
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/* We check the new mask on the same chars in the next iteration */
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continue;
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}
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p += 4;
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}
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while (p < end) {
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if (p[0] & mask) {
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if (mask == mask_limit) {
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/* Limit reached */
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return max_char_limit;
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}
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if (mask == MASK_ASCII) {
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max_char = MAX_CHAR_UCS1;
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mask = MASK_UCS1;
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}
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else {
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/* mask can't be MASK_UCS2 because of mask_limit above */
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assert(mask == MASK_UCS1);
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max_char = MAX_CHAR_UCS2;
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mask = MASK_UCS2;
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}
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/* We check the new mask on the same chars in the next iteration */
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continue;
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}
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p++;
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}
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return max_char;
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}
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#undef MASK_ASCII
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#undef MASK_UCS1
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#undef MASK_UCS2
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#undef MAX_CHAR_ASCII
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#undef MAX_CHAR_UCS1
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#undef MAX_CHAR_UCS2
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#undef MAX_CHAR_UCS4
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#endif /* STRINGLIB_SIZEOF_CHAR == 1 */
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