Function str_gsub

3rd/lua-5.4.3/src/lstrlib.c:942–983

static int str_gsub (lua_State *L) {
  size_t srcl, lp;
  const char *src = luaL_checklstring(L, 1, &srcl);  /* subject */
  const char *p = luaL_checklstring(L, 2, &lp);  /* pattern */
  const char *lastmatch = NULL;  /* end of last match */
  int tr = lua_type(L, 3);  /* replacement type */
  lua_Integer max_s = luaL_optinteger(L, 4, srcl + 1);  /* max replacements */
  int anchor = (*p == '^');
  lua_Integer n = 0;  /* replacement count */
  int changed = 0;  /* change flag */
  MatchState ms;
  luaL_Buffer b;
  luaL_argexpected(L, tr == LUA_TNUMBER || tr == LUA_TSTRING ||
                   tr == LUA_TFUNCTION || tr == LUA_TTABLE, 3,
                      "string/function/table");
  luaL_buffinit(L, &b);
  if (anchor) {
    p++; lp--;  /* skip anchor character */
  }
  prepstate(&ms, L, src, srcl, p, lp);
  while (n < max_s) {
    const char *e;
    reprepstate(&ms);  /* (re)prepare state for new match */
    if ((e = match(&ms, src, p)) != NULL && e != lastmatch) {  /* match? */
      n++;
      changed = add_value(&ms, &b, src, e, tr) | changed;
      src = lastmatch = e;
    }
    else if (src < ms.src_end)  /* otherwise, skip one character */
      luaL_addchar(&b, *src++);
    else break;  /* end of subject */
    if (anchor) break;
  }
  if (!changed)  /* no changes? */
    lua_pushvalue(L, 1);  /* return original string */
  else {  /* something changed */
    luaL_addlstring(&b, src, ms.src_end-src);
    luaL_pushresult(&b);  /* create and return new string */
  }
  lua_pushinteger(L, n);  /* number of substitutions */
  return 2;
}

/* }====================================================== */