unicode-case-fold.py

#!/usr/bin/env python
"""
Unicode case folding database conversion utility

Parses the database and generates a C++ function which implements the case
folding algorithm. The database entries are of the form:

  <code>; <status>; <mapping>; # <name>

<status> can be one of four characters:
  C - Common mappings
  S - mappings for Simple case folding
  F - mappings for Full case folding
  T - special case for Turkish I characters

Right now this generates a function which implements simple case folding (C+S
entries).
"""

from __future__ import print_function

import sys
import re
try:
    from urllib.request import urlopen
except ImportError:
    from urllib2 import urlopen


# This variable will body of the mappings function
body = ""

# Reads file line-by-line, extracts Common and Simple case fold mappings and
# returns a (from_char, to_char, from_name) tuple.
def mappings(f):
    previous_from = -1
    expr = re.compile(r'^(.*); [CS]; (.*); # (.*)')
    for line in f:
        m = expr.match(line)
        if not m: continue
        from_char = int(m.group(1), 16)
        to_char = int(m.group(2), 16)
        from_name = m.group(3)

        if from_char <= previous_from:
            raise Exception("Duplicate or unsorted characters in input")
        yield from_char, to_char, from_name
        previous_from = from_char

# Computes the shift (to_char - from_char) in a mapping.
def shift(mapping):
    return mapping[1] - mapping[0]

# Computes the stride (from_char2 - from_char1) of two mappings.
def stride2(mapping1, mapping2):
    return mapping2[0] - mapping1[0]

# Computes the stride of a list of mappings. The list should have at least two
# mappings. All mappings in the list are assumed to have the same stride.
def stride(block):
    return stride2(block[0], block[1])


# b is a list of mappings. All the mappings are assumed to have the same
# shift and the stride between adjecant mappings (if any) is constant.
def dump_block(b):
    global body

    if len(b) == 1:
        # Special case for handling blocks of length 1. We don't even need to
        # emit the "if (C < X) return C" check below as all characters in this
        # range will be caught by the "C < X" check emitted by the first
        # non-trivial block.
        body  += "  // {2}\n  if (C == {0:#06x})\n    return {1:#06x};\n".format(*b[0])
        return

    first = b[0][0]
    last = first + stride(b) * (len(b)-1)
    modulo = first % stride(b)

    # All characters before this block map to themselves.
    body += "  if (C < {0:#06x})\n    return C;\n".format(first)
    body += "  // {0} characters\n".format(len(b))

    # Generic pattern: check upper bound (lower bound is checked by the "if"
    # above) and modulo of C, return C+shift.
    pattern = "  if (C <= {0:#06x} && C % {1} == {2})\n    return C + {3};\n"

    if stride(b) == 2 and shift(b[0]) == 1 and modulo == 0:
        # Special case:
        # We can elide the modulo-check because the expression "C|1" will map
        # the intervening characters to themselves.
        pattern = "  if (C <= {0:#06x})\n    return C | 1;\n"
    elif stride(b) == 1:
        # Another special case: X % 1 is always zero, so don't emit the
        # modulo-check.
        pattern = "  if (C <= {0:#06x})\n    return C + {3};\n"

    body += pattern.format(last, stride(b), modulo, shift(b[0]))

current_block = []
f = urlopen(sys.argv[1])
for m in mappings(f):
    if len(current_block) == 0:
        current_block.append(m)
        continue

    if shift(current_block[0]) != shift(m):
        # Incompatible shift, start a new block.
        dump_block(current_block)
        current_block = [m]
        continue

    if len(current_block) == 1 or stride(current_block) == stride2(current_block[-1], m):
        current_block.append(m)
        continue

    # Incompatible stride, start a new block.
    dump_block(current_block)
    current_block = [m]
f.close()

dump_block(current_block)

print('//===---------- Support/UnicodeCaseFold.cpp -------------------------------===//')
print('//')
print('// This file was generated by utils/unicode-case-fold.py from the Unicode')
print('// case folding database at')
print('//   ', sys.argv[1])
print('//')
print('// To regenerate this file, run:')
print('//   utils/unicode-case-fold.py \\')
print('//     "{}" \\'.format(sys.argv[1]))
print('//     > lib/Support/UnicodeCaseFold.cpp')
print('//')
print('//===----------------------------------------------------------------------===//')
print('')
print('#include "llvm/Support/Unicode.h"')
print('')
print("int llvm::sys::unicode::foldCharSimple(int C) {")
print(body)
print("  return C;")
print("}")