libc/bionic/wcwidth.cpp

/*
 * Copyright (C) 2017 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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 */

#include <wchar.h>

#include "private/icu4x.h"

int wcwidth(wchar_t wc) {
  // Fast-path ASCII.
  if (wc >= 0x20 && wc < 0x7f) return 1;

  // ASCII NUL is a special case.
  if (wc == 0) return 0;

  // C0.
  if (wc < ' ' || (wc >= 0x7f && wc <= 0xa0)) return -1;

  // Now for the i18n part. This isn't defined or standardized, so a lot of the choices are
  // pretty arbitrary. See https://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c for more details.

  // Fancy unicode control characters?
  switch (__icu4x_bionic_general_category(wc)) {
    case U_CONTROL_CHAR:
      return -1;
    case U_NON_SPACING_MARK:
    case U_ENCLOSING_MARK:
      return 0;
    case U_FORMAT_CHAR:
      // A special case for soft hyphen (U+00AD) to match historical practice.
      // See the tests for more commentary.
      return (wc == 0x00ad) ? 1 : 0;
  }

  // Medial and final jamo render as zero width when used correctly,
  // so we handle them specially rather than relying on East Asian Width.
  switch (__icu4x_bionic_hangul_syllable_type(wc)) {
    case U_HST_VOWEL_JAMO:
    case U_HST_TRAILING_JAMO:
      return 0;
    case U_HST_LEADING_JAMO:
    case U_HST_LV_SYLLABLE:
    case U_HST_LVT_SYLLABLE:
      return 2;
  }

  // Hangeul choseong filler U+115F is default ignorable, so we check default
  // ignorability only after we've already handled Hangeul jamo above.
  if (__icu4x_bionic_is_default_ignorable_code_point(wc)) return 0;

  // A few weird special cases where EastAsianWidth is not helpful for us.
  if (wc >= 0x3248 && wc <= 0x4dff) {
    // Circled two-digit CJK "speed sign" numbers. EastAsianWidth is ambiguous,
    // but wide makes more sense.
    if (wc <= 0x324f) return 2;
    // Hexagrams. EastAsianWidth is neutral, but wide seems better.
    if (wc >= 0x4dc0) return 2;
  }

  // The EastAsianWidth property is at least defined by the Unicode standard!
  // https://www.unicode.org/reports/tr11/
  switch (__icu4x_bionic_east_asian_width(wc)) {
    case U_EA_AMBIGUOUS:
    case U_EA_HALFWIDTH:
    case U_EA_NARROW:
    case U_EA_NEUTRAL:
      return 1;
    case U_EA_FULLWIDTH:
    case U_EA_WIDE:
      return 2;
  }

  return 0;
}