mruby-mruby/src/symbol.c

/*
** symbol.c - Symbol class
**
** See Copyright Notice in mruby.h
*/

#include <string.h>
#include <mruby.h>
#include <mruby/string.h>
#include <mruby/dump.h>
#include <mruby/class.h>
#include <mruby/internal.h>
#include <mruby/presym.h>

#ifndef MRB_NO_PRESYM

#ifndef MRB_PRESYM_SCANNING
/* const uint16_t presym_length_table[]   */
/* const char * const presym_name_table[] */
# include <mruby/presym/table.h>
#endif

static mrb_sym
presym_find(const char *name, size_t len)
{
  if (presym_length_table[MRB_PRESYM_MAX-1] < len) return 0;

  mrb_sym presym_size = MRB_PRESYM_MAX;
  for (mrb_sym start = 0; presym_size != 0; presym_size/=2) {
    mrb_sym idx = start+presym_size/2;
    int cmp = (int)len-(int)presym_length_table[idx];
    if (cmp == 0) {
      cmp = memcmp(name, presym_name_table[idx], len);
      if (cmp == 0) return idx+1;
    }
    if (0 < cmp) {
      start = ++idx;
      --presym_size;
    }
  }
  return 0;
}

static const char*
presym_sym2name(mrb_sym sym, mrb_int *lenp)
{
  if (sym > MRB_PRESYM_MAX) return NULL;
  if (lenp) *lenp = presym_length_table[sym-1];
  return presym_name_table[sym-1];
}

#endif  /* MRB_NO_PRESYM */

/* ------------------------------------------------------ */

/* LSB pointer tagging for literal flags */
#define SYMTBL_LITERAL_FLAG ((uintptr_t)1)

/* Extract clean pointer for memory operations */
static inline const char*
symtbl_get_ptr(const char *tagged_ptr)
{
  return (const char*)((uintptr_t)tagged_ptr & ~SYMTBL_LITERAL_FLAG);
}

/* Check if symbol is literal by testing LSB */
static inline mrb_bool
symtbl_is_literal(const char *tagged_ptr)
{
  return ((uintptr_t)tagged_ptr & SYMTBL_LITERAL_FLAG) != 0;
}

/* Create tagged pointer for literal string - with alignment verification */
static inline const char*
symtbl_tag_literal(const char *ptr)
{
  mrb_assert(((uintptr_t)ptr & 1) == 0);  /* Assert alignment */
  return (const char*)((uintptr_t)ptr | SYMTBL_LITERAL_FLAG);
}

static void
sym_validate_len(mrb_state *mrb, size_t len)
{
  if (len >= UINT16_MAX) {
    mrb_raise(mrb, E_ARGUMENT_ERROR, "symbol length too long");
  }
}

/* Chunk-based string pool for heap-allocated symbol names */
#define MRB_SYM_POOL_CHUNK_SIZE 4096

struct sym_pool_chunk {
  struct sym_pool_chunk *next;
  size_t used;
  char buf[];  /* flexible array */
};

static char*
sym_pool_alloc(mrb_state *mrb, size_t size)
{
  /* round up to even size to keep pointers even-aligned (LSB tagging) */
  size_t asize = (size + 1) & ~(size_t)1;
  struct sym_pool_chunk *chunk = (struct sym_pool_chunk*)mrb->sym_pool;
  if (chunk && chunk->used + asize <= MRB_SYM_POOL_CHUNK_SIZE) {
    char *p = chunk->buf + chunk->used;
    chunk->used += asize;
    return p;
  }
  size_t csize = asize > MRB_SYM_POOL_CHUNK_SIZE ? asize : MRB_SYM_POOL_CHUNK_SIZE;
  chunk = (struct sym_pool_chunk*)mrb_malloc(mrb,
    offsetof(struct sym_pool_chunk, buf) + csize);
  chunk->next = (struct sym_pool_chunk*)mrb->sym_pool;
  chunk->used = asize;
  mrb->sym_pool = (void*)chunk;
  return chunk->buf;
}

/* Hash table for symbols (allocated on demand when symbols exceed threshold) */
struct mrb_sym_hash_table {
  uint8_t *symlink;         /* collision resolution chains */
  mrb_sym buckets[256];     /* hash buckets */
};

#ifdef MRB_USE_ALL_SYMBOLS
# define SYMBOL_INLINE_P(sym) FALSE
# define sym_inline_pack(name, len) 0
# define sym_inline_unpack(sym, buf, lenp) NULL
#else
# define SYMBOL_INLINE_P(sym) ((sym) >= (1<<20))

static const char pack_table[] = "_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

static mrb_sym
sym_inline_pack(const char *name, size_t len)
{
  const size_t pack_length_max = 4;
  mrb_sym sym = 0;

  if (len > pack_length_max) return 0; /* too long */
  if (len == 0) return 0; /* empty string */
  for (size_t i=0; i<len; i++) {
    char c = name[i];
    if (c == 0) return 0;       /* NUL in name */
    const char *p = strchr(pack_table, (int)c);
    if (p == 0) return 0;       /* non alnum char */

    uint32_t bits = (uint32_t)(p - pack_table)+1;
    sym |= bits<<(20-i*6);
  }
  mrb_assert(SYMBOL_INLINE_P(sym));
  return sym;
}

static const char*
sym_inline_unpack(mrb_sym sym, char *buf, mrb_int *lenp)
{
  const size_t pack_length_max = 4;
  size_t i;

  mrb_assert(SYMBOL_INLINE_P(sym));

  for (i=0; i<pack_length_max; i++) {
    uint32_t bits = sym>>(20-i*6) & 0x3f;
    if (bits == 0) break;
    buf[i] = pack_table[bits-1];
  }
  buf[i] = '\0';
  if (lenp) *lenp = i;
  return buf;
}
#endif

/* Check if using hash table mode */
static inline mrb_bool
using_hash_table(mrb_state *mrb)
{
  return mrb->symhash != NULL;
}

static mrb_bool
sym_check(mrb_state *mrb, const char *name, size_t len, mrb_sym i)
{
  const char *tagged_ptr = mrb->symtbl[i];
  const char *symname = symtbl_get_ptr(tagged_ptr);  /* Untag for access */
  size_t symlen;

  if (symtbl_is_literal(tagged_ptr)) {
    symlen = strlen(symname);
  }
  else {
    /* length in BER */
    symlen = mrb_packed_int_decode((const uint8_t*)symname, (const uint8_t**)&symname);
  }
  if (len == symlen && memcmp(symname, name, len) == 0) {
    return TRUE;
  }
  return FALSE;
}

static mrb_sym
find_symbol_linear(mrb_state *mrb, const char *name, size_t len)
{
  mrb_sym i;

  for (i = 1; i <= mrb->symidx; i++) {
    if (sym_check(mrb, name, len, i)) {
      return (i + MRB_PRESYM_MAX);
    }
  }
  return 0;
}

static mrb_sym
find_symbol_hash(mrb_state *mrb, const char *name, size_t len, uint8_t *hashp)
{
  mrb_sym i;
  uint8_t hash;
  struct mrb_sym_hash_table *ht = mrb->symhash;

  hash = mrb_byte_hash((const uint8_t*)name, len);
  if (hashp) *hashp = hash;

  i = ht->buckets[hash];
  if (i == 0) return 0;
  for (;;) {
    if (sym_check(mrb, name, len, i)) {
      return (i+MRB_PRESYM_MAX);
    }
    uint8_t diff = ht->symlink[i];
    if (diff == 0xff) {
      i -= 0xff;
      while (i > 0) {
        if (sym_check(mrb, name, len, i)) {
          return (i+MRB_PRESYM_MAX);
        }
        i--;
      }
      return 0;
    }
    if (diff == 0) return 0;
    i -= diff;
  }
  return 0;
}

static mrb_sym
find_symbol(mrb_state *mrb, const char *name, size_t len, uint8_t *hashp)
{
  mrb_sym i;

#ifndef MRB_NO_PRESYM
  /* presym */
  i = presym_find(name, len);
  if (i > 0) return i;
#endif

  /* inline symbol */
  i = sym_inline_pack(name, len);
  if (i > 0) return i;

  if (using_hash_table(mrb)) {
    /* Hash table mode - O(1) average case */
    return find_symbol_hash(mrb, name, len, hashp);
  }
  else {
    /* Linear mode - O(n) but fast for small n */
    if (hashp) *hashp = mrb_byte_hash((const uint8_t*)name, len);
    return find_symbol_linear(mrb, name, len);
  }
}

static void
migrate_to_hash_table(mrb_state *mrb)
{
  struct mrb_sym_hash_table *ht;
  mrb_sym i;

  mrb_assert(mrb->symhash == NULL);
  mrb_assert(mrb->symidx >= MRB_SYMBOL_LINEAR_THRESHOLD);

  /* Allocate hash table structure */
  ht = (struct mrb_sym_hash_table*)mrb_calloc(mrb, 1, sizeof(struct mrb_sym_hash_table));
  ht->symlink = (uint8_t*)mrb_calloc(mrb, mrb->symcapa, sizeof(uint8_t));

  /* Rebuild hash table from existing linear data */
  for (i = 1; i <= mrb->symidx; i++) {
    const char *tagged_ptr = mrb->symtbl[i];
    const char *name = symtbl_get_ptr(tagged_ptr);
    size_t len;
    uint8_t hash;

    /* Get name and length from tagged pointer */
    if (symtbl_is_literal(tagged_ptr)) {
      len = strlen(name);
    }
    else {
      /* This is a packed length string */
      len = mrb_packed_int_decode((const uint8_t*)name, (const uint8_t**)&name);
    }

    hash = mrb_byte_hash((const uint8_t*)name, len);

    /* Build collision chain */
    if (ht->buckets[hash] != 0) {
      mrb_sym diff = i - ht->buckets[hash];
      ht->symlink[i] = (diff > 0xff) ? 0xff : (uint8_t)diff;
    }
    else {
      ht->symlink[i] = 0;
    }
    ht->buckets[hash] = i;
  }

  mrb->symhash = ht;
}

static mrb_sym
sym_intern_common(mrb_state *mrb, const char *name, size_t len, mrb_bool lit)
{
  mrb_sym sym;

  sym = mrb->symidx + 1;
  if (mrb->symcapa <= sym) {
    size_t symcapa = mrb->symcapa;
    if (symcapa == 0) symcapa = 100;
    else symcapa = (size_t)(symcapa * 6 / 5);
    mrb->symtbl = (const char**)mrb_realloc(mrb, (void*)mrb->symtbl, sizeof(char*)*symcapa);
    if (using_hash_table(mrb)) {
      struct mrb_sym_hash_table *ht = mrb->symhash;
      ht->symlink = (uint8_t*)mrb_realloc(mrb, ht->symlink, symcapa);
    }
    mrb->symcapa = symcapa;
  }

  lit = lit || mrb_ro_data_p(name);
  if (lit && name[len] == 0 && strlen(name) == len) {
    if (((uintptr_t)name & 1) != 0) {
      /* Fallback: unaligned literal, allocate heap copy */
      goto heap_allocation;
    }
    mrb->symtbl[sym] = symtbl_tag_literal(name);
  }
  else {
  heap_allocation:;
    /* Always heap-allocate when not explicitly literal */
    uint32_t ulen = (uint32_t)len;
    size_t ilen = mrb_packed_int_len(ulen);
    char *p = sym_pool_alloc(mrb, len+ilen+1);
    mrb_packed_int_encode(ulen, (uint8_t*)p);
    memcpy(p+ilen, name, len);
    p[ilen+len] = 0;
    mrb->symtbl[sym] = p;  /* Untagged = heap */
  }

  mrb->symidx = sym;
  return sym;
}

static mrb_sym
sym_intern_linear_mode(mrb_state *mrb, const char *name, size_t len, mrb_bool lit)
{
  mrb_sym sym = sym_intern_common(mrb, name, len, lit);
  return (sym+MRB_PRESYM_MAX);
}

static mrb_sym
sym_intern_hash_mode(mrb_state *mrb, const char *name, size_t len, mrb_bool lit)
{
  mrb_sym sym = sym_intern_common(mrb, name, len, lit);
  struct mrb_sym_hash_table *ht = mrb->symhash;
  uint8_t hash = mrb_byte_hash((const uint8_t*)name, len);

  if (ht->buckets[hash]) {
    mrb_sym i = sym - ht->buckets[hash];
    if (i > 0xff)
      ht->symlink[sym] = 0xff;
    else
      ht->symlink[sym] = i;
  }
  else {
    ht->symlink[sym] = 0;
  }
  ht->buckets[hash] = sym;

  return (sym+MRB_PRESYM_MAX);
}

static mrb_sym
sym_intern(mrb_state *mrb, const char *name, size_t len, mrb_bool lit)
{
  mrb_sym sym;

  sym_validate_len(mrb, len);
  sym = find_symbol(mrb, name, len, NULL);
  if (sym > 0) return sym;

  /* Check if we need to migrate to hash table */
  if (!using_hash_table(mrb) && mrb->symidx >= MRB_SYMBOL_LINEAR_THRESHOLD) {
    migrate_to_hash_table(mrb);
  }

  /* Add new symbol using current mode */
  if (using_hash_table(mrb)) {
    return sym_intern_hash_mode(mrb, name, len, lit);
  }
  else {
    return sym_intern_linear_mode(mrb, name, len, lit);
  }
}

/*
 * Interns a string, creating a symbol from it if it doesn't already exist,
 * or returning the existing symbol if it does.
 *
 * mrb: The mruby state.
 * name: The string to intern.
 * len: The length of the string.
 *
 * Returns the interned symbol.
 */
MRB_API mrb_sym
mrb_intern(mrb_state *mrb, const char *name, size_t len)
{
  return sym_intern(mrb, name, len, FALSE);
}

/*
 * Interns a static string, creating a symbol from it.
 * This function is similar to mrb_intern, but it assumes that the given
 * string is static and will not be freed.
 *
 * mrb: The mruby state.
 * name: The static string to intern.
 * len: The length of the string.
 *
 * Returns the interned symbol.
 */
MRB_API mrb_sym
mrb_intern_static(mrb_state *mrb, const char *name, size_t len)
{
  return sym_intern(mrb, name, len, TRUE);
}

/*
 * Interns a C string (null-terminated), creating a symbol from it.
 * This function is a convenience wrapper around mrb_intern that
 * automatically calculates the length of the string.
 *
 * mrb: The mruby state.
 * name: The C string to intern.
 *
 * Returns the interned symbol.
 */
MRB_API mrb_sym
mrb_intern_cstr(mrb_state *mrb, const char *name)
{
  return mrb_intern(mrb, name, strlen(name));
}

/*
 * Interns an mruby string value, creating a symbol from it.
 *
 * mrb: The mruby state.
 * str: The mruby string value to intern.
 *
 * Returns the interned symbol.
 */
MRB_API mrb_sym
mrb_intern_str(mrb_state *mrb, mrb_value str)
{
  return mrb_intern(mrb, RSTRING_PTR(str), RSTRING_LEN(str));
}

/*
 * Checks if a symbol already exists for the given string.
 *
 * mrb: The mruby state.
 * name: The string to check.
 * len: The length of the string.
 *
 * Returns the symbol if it exists, otherwise 0.
 */
MRB_API mrb_sym
mrb_intern_check(mrb_state *mrb, const char *name, size_t len)
{
  mrb_sym sym;

  sym_validate_len(mrb, len);
  sym = find_symbol(mrb, name, len, NULL);
  if (sym > 0) return sym;
  return 0;
}

/*
 * Checks if a symbol already exists for the given string.
 *
 * mrb: The mruby state.
 * name: The string to check.
 * len: The length of the string.
 *
 * Returns the symbol as an mrb_value if it exists, otherwise a nil value.
 */
MRB_API mrb_value
mrb_check_intern(mrb_state *mrb, const char *name, size_t len)
{
  mrb_sym sym = mrb_intern_check(mrb, name, len);
  if (sym == 0) return mrb_nil_value();
  return mrb_symbol_value(sym);
}

/*
 * Checks if a symbol already exists for the given C string (null-terminated).
 * This function is a convenience wrapper around mrb_intern_check that
 * automatically calculates the length of the string.
 *
 * mrb: The mruby state.
 * name: The C string to check.
 *
 * Returns the symbol if it exists, otherwise 0.
 */
MRB_API mrb_sym
mrb_intern_check_cstr(mrb_state *mrb, const char *name)
{
  return mrb_intern_check(mrb, name, strlen(name));
}

/*
 * Checks if a symbol already exists for the given C string (null-terminated).
 * This function is similar to mrb_intern_check_cstr, but returns the result
 * as an mrb_value (either the symbol or nil).
 *
 * mrb: The mruby state.
 * name: The C string to check.
 *
 * Returns the symbol as an mrb_value if it exists, otherwise a nil value.
 */
MRB_API mrb_value
mrb_check_intern_cstr(mrb_state *mrb, const char *name)
{
  mrb_sym sym = mrb_intern_check_cstr(mrb, name);
  if (sym == 0) return mrb_nil_value();
  return mrb_symbol_value(sym);
}

/*
 * Checks if a symbol already exists for the given mruby string value.
 *
 * mrb: The mruby state.
 * str: The mruby string value to check.
 *
 * Returns the symbol if it exists, otherwise 0.
 */
MRB_API mrb_sym
mrb_intern_check_str(mrb_state *mrb, mrb_value str)
{
  return mrb_intern_check(mrb, RSTRING_PTR(str), RSTRING_LEN(str));
}

/*
 * Checks if a symbol already exists for the given mruby string value.
 * This function is similar to mrb_intern_check_str, but returns the result
 * as an mrb_value (either the symbol or nil).
 *
 * mrb: The mruby state.
 * str: The mruby string value to check.
 *
 * Returns the symbol as an mrb_value if it exists, otherwise a nil value.
 */
MRB_API mrb_value
mrb_check_intern_str(mrb_state *mrb, mrb_value str)
{
  mrb_sym sym = mrb_intern_check_str(mrb, str);
  if (sym == 0) return mrb_nil_value();
  return mrb_symbol_value(sym);
}

static const char*
sym2name_len(mrb_state *mrb, mrb_sym sym, char *buf, mrb_int *lenp)
{
  if (sym == 0) goto outofsym;
  if (SYMBOL_INLINE_P(sym)) return sym_inline_unpack(sym, buf, lenp);

#ifndef MRB_NO_PRESYM
  {
    const char *name = presym_sym2name(sym, lenp);
    if (name) return name;
  }
#endif
  sym -= MRB_PRESYM_MAX;

  if (mrb->symidx < sym) {
  outofsym:
    if (lenp) *lenp = 0;
    return NULL;
  }

  const char *tagged_ptr = mrb->symtbl[sym];
  const char *symname = symtbl_get_ptr(tagged_ptr);  /* Untag for access */

  if (!symtbl_is_literal(tagged_ptr)) {
    uint32_t len = mrb_packed_int_decode((const uint8_t*)symname, (const uint8_t**)&symname);
    if (lenp) *lenp = (mrb_int)len;
  }
  else if (lenp) {
    *lenp = (mrb_int)strlen(symname);
  }
  return symname;
}

/*
 * Retrieves the name and length of a symbol.
 *
 * mrb: The mruby state.
 * sym: The symbol to retrieve the name and length for.
 * lenp: A pointer to an mrb_int where the length of the symbol name will be stored.
 *       This can be NULL if the length is not needed.
 *
 * Returns a pointer to the C string representing the symbol's name,
 * or NULL if the symbol is invalid.
 * For inline symbols, the name is copied to an internal buffer (mrb->symbuf)
 * unless MRB_USE_ALL_SYMBOLS is defined.
 */
MRB_API const char*
mrb_sym_name_len(mrb_state *mrb, mrb_sym sym, mrb_int *lenp)
{
#ifdef MRB_USE_ALL_SYMBOLS
  return sym2name_len(mrb, sym, NULL, lenp);
#else
  return sym2name_len(mrb, sym, mrb->symbuf, lenp);
#endif
}

void
mrb_free_symtbl(mrb_state *mrb)
{
  /* Free symbol string pool chunks */
  struct sym_pool_chunk *chunk = (struct sym_pool_chunk*)mrb->sym_pool;
  while (chunk) {
    struct sym_pool_chunk *next = chunk->next;
    mrb_free(mrb, chunk);
    chunk = next;
  }
  mrb->sym_pool = NULL;

  mrb_free(mrb, (void*)mrb->symtbl);

  /* Free hash table if allocated */
  if (mrb->symhash) {
    mrb_free(mrb, mrb->symhash->symlink);
    mrb_free(mrb, mrb->symhash);
    mrb->symhash = NULL;
  }
}

void
mrb_init_symtbl(mrb_state *mrb)
{
  /* Initialize in linear mode - hash table allocated on demand */
  mrb->symhash = NULL;
  mrb->sym_pool = NULL;
}

/**********************************************************************
 * Document-class: Symbol
 *
 *  `Symbol` objects represent names and some strings
 *  inside the Ruby
 *  interpreter. They are generated using the `:name` and
 *  `:"string"` literals
 *  syntax, and by the various `to_sym` methods. The same
 *  `Symbol` object will be created for a given name or string
 *  for the duration of a program's execution, regardless of the context
 *  or meaning of that name. Thus if `Fred` is a constant in
 *  one context, a method in another, and a class in a third, the
 *  `Symbol` `:Fred` will be the same object in
 *  all three contexts.
 *
 *     module One
 *       class Fred
 *       end
 *       $f1 = :Fred
 *     end
 *     module Two
 *       Fred = 1
 *       $f2 = :Fred
 *     end
 *     def Fred()
 *     end
 *     $f3 = :Fred
 *     $f1.object_id   #=> 2514190
 *     $f2.object_id   #=> 2514190
 *     $f3.object_id   #=> 2514190
 *
 */

/* 15.2.11.3.2  */
/* 15.2.11.3.3  */
/*
 *  call-seq:
 *     sym.to_s      -> string
 *
 *  Returns the name or string corresponding to *sym*.
 *
 *     :fred.to_s   #=> "fred"
 */
static mrb_value
sym_to_s(mrb_state *mrb, mrb_value sym)
{
  return mrb_sym_str(mrb, mrb_symbol(sym));
}

/*
 *  call-seq:
 *     sym.name   -> string
 *
 *  Returns the name or string corresponding to *sym*. Unlike #to_s, the
 *  returned string is frozen.
 *
 *     :fred.name         #=> "fred"
 *     :fred.name.frozen? #=> true
 */
static mrb_value
sym_name(mrb_state *mrb, mrb_value vsym)
{
  mrb_sym sym = mrb_symbol(vsym);
  mrb_int len;
  const char *name = mrb_sym_name_len(mrb, sym, &len);

  mrb_assert(name != NULL);
  if (SYMBOL_INLINE_P(sym)) {
    return mrb_str_new_frozen(mrb, name, len);
  }
  return mrb_str_new_static_frozen(mrb, name, len);
}

/* 15.2.11.3.4  */
/*
 * Document-method: Symbol#to_sym
 *
 * call-seq:
 *   sym.to_sym   -> sym
 *   sym.intern   -> sym
 *
 * In general, `to_sym` returns the `Symbol` corresponding
 * to an object. As *sym* is already a symbol, `self` is returned
 * in this case.
 */

/* 15.2.11.3.5(x)  */
/*
 *  call-seq:
 *     sym.inspect    -> string
 *
 *  Returns the representation of *sym* as a symbol literal.
 *
 *     :fred.inspect   #=> ":fred"
 */

#if __STDC__
# define SIGN_EXTEND_CHAR(c) ((signed char)(c))
#else  /* not __STDC__ */
/* As in Harbison and Steele.  */
# define SIGN_EXTEND_CHAR(c) ((((unsigned char)(c)) ^ 128) - 128)
#endif
#define is_identchar(c) (SIGN_EXTEND_CHAR(c)!=-1&&(ISALNUM(c) || (c) == '_'))

static mrb_bool
is_special_global_name(const char* m)
{
  switch (*m) {
    case '~': case '*': case '$': case '?': case '!': case '@':
    case '/': case '\\': case ';': case ',': case '.': case '=':
    case ':': case '<': case '>': case '\"':
    case '&': case '`': case '\'': case '+':
    case '0':
      m++;
      break;
    case '-':
      m++;
      if (is_identchar(*m)) m += 1;
      break;
    default:
      if (!ISDIGIT(*m)) return FALSE;
      do m++; while (ISDIGIT(*m));
      break;
  }
  return !*m;
}

static mrb_bool
symname_p(const char *name)
{
  const char *m = name;
  mrb_bool localid = FALSE;

  if (!m) return FALSE;
  switch (*m) {
    case '\0':
      return FALSE;

    case '$':
      if (is_special_global_name(++m)) return TRUE;
      goto id;

    case '@':
      if (*++m == '@') ++m;
      goto id;

    case '<':
      switch (*++m) {
        case '<': ++m; break;
        case '=': if (*++m == '>') m++; break;
        default: break;
      }
      break;

    case '>':
      switch (*++m) {
        case '>': case '=': ++m; break;
        default: break;
      }
      break;

    case '=':
      switch (*++m) {
        case '~': m++; break;
        case '=': if (*++m == '=') m++; break;
        default: return FALSE;
      }
      break;

    case '*':
      if (*++m == '*') m++;
      break;
    case '!':
      switch (*++m) {
        case '=': case '~': m++;
      }
      break;
    case '+': case '-':
      if (*++m == '@') m++;
      break;
    case '|':
      if (*++m == '|') m++;
      break;
    case '&':
      if (*++m == '&') m++;
      break;

    case '^': case '/': case '%': case '~': case '`':
      m++;
      break;

    case '[':
      if (*++m != ']') return FALSE;
      if (*++m == '=') m++;
      break;

    default:
      localid = !ISUPPER(*m);
id:
      if (*m != '_' && !ISALPHA(*m)) return FALSE;
      while (is_identchar(*m)) m += 1;
      if (localid) {
        switch (*m) {
          case '!': case '?': case '=': m++;
          default: break;
        }
      }
      break;
  }
  return *m ? FALSE : TRUE;
}

static mrb_value
sym_inspect(mrb_state *mrb, mrb_value sym)
{
  mrb_sym id = mrb_symbol(sym);
  mrb_int len;
  const char *name = mrb_sym_name_len(mrb, id, &len);
  mrb_value str = mrb_str_new(mrb, NULL, len+1);
  char *sp = RSTRING_PTR(str);

  sp[0] = ':';
  memcpy(sp+1, name, len);
  mrb_assert_int_fit(mrb_int, len, size_t, SIZE_MAX);
  if (!symname_p(name) || strlen(name) != (size_t)len) {
    str = mrb_str_inspect(mrb, str);
    sp = RSTRING_PTR(str);
    sp[0] = ':';
    sp[1] = '"';
  }
#ifdef MRB_UTF8_STRING
  if (SYMBOL_INLINE_P(id)) RSTR_SET_ASCII_FLAG(mrb_str_ptr(str));
#endif
  return str;
}

/*
 * Converts a symbol to an mruby string value.
 *
 * mrb: The mruby state.
 * sym: The symbol to convert.
 *
 * Returns the mruby string value corresponding to the symbol.
 * If the symbol is an inline symbol, a new string is created.
 * Otherwise, a static string (sharing the symbol's name buffer) is returned.
 * Returns an undefined value if the symbol is invalid (though this should not happen).
 */
MRB_API mrb_value
mrb_sym_str(mrb_state *mrb, mrb_sym sym)
{
  mrb_int len;
  const char *name = mrb_sym_name_len(mrb, sym, &len);

  if (!name) return mrb_undef_value(); /* can't happen */
  if (SYMBOL_INLINE_P(sym)) {
    mrb_value str = mrb_str_new(mrb, name, len);
    RSTR_SET_ASCII_FLAG(mrb_str_ptr(str));
    return str;
  }
  return mrb_str_new_static(mrb, name, len);
}

static const char*
sym_cstr(mrb_state *mrb, mrb_sym sym, mrb_bool dump)
{
  mrb_int len;
  const char *name = mrb_sym_name_len(mrb, sym, &len);

  if (!name) return NULL;
  if (strlen(name) == (size_t)len && (!dump || symname_p(name))) {
    return name;
  }
  else {
    mrb_value str = mrb_str_new_static(mrb, name, len);
    str = mrb_str_dump(mrb, str);
    return RSTRING_PTR(str);
  }
}

/*
 * Retrieves the C string representation of a symbol's name.
 *
 * mrb: The mruby state.
 * sym: The symbol to retrieve the name for.
 *
 * Returns a pointer to the C string representing the symbol's name.
 * Returns NULL if the symbol is invalid.
 * If the symbol's name contains null bytes or is not a valid identifier
 * for direct use (based on internal checks in sym_cstr), this function
 * might return a "dumped" (quoted and escaped) version of the name.
 */
MRB_API const char*
mrb_sym_name(mrb_state *mrb, mrb_sym sym)
{
  return sym_cstr(mrb, sym, FALSE);
}

/*
 * Retrieves the C string representation of a symbol's name, suitable for dumping.
 * This version is intended for producing a string that can be safely outputted,
 * for example, in debugging or serialization contexts. It may quote or escape
 * the symbol name if it's not a simple identifier.
 *
 * mrb: The mruby state.
 * sym: The symbol to retrieve the dump name for.
 *
 * Returns a pointer to the C string representing the symbol's name for dumping.
 * Returns NULL if the symbol is invalid.
 */
MRB_API const char*
mrb_sym_dump(mrb_state *mrb, mrb_sym sym)
{
  return sym_cstr(mrb, sym, TRUE);
}

#define lesser(a,b) (((a)>(b))?(b):(a))

static mrb_value
sym_cmp(mrb_state *mrb, mrb_value s1)
{
  mrb_value s2 = mrb_get_arg1(mrb);
  mrb_sym sym1, sym2;

  if (!mrb_symbol_p(s2)) return mrb_nil_value();
  sym1 = mrb_symbol(s1);
  sym2 = mrb_symbol(s2);
  if (sym1 == sym2) return mrb_fixnum_value(0);
  else {
    const char *p1, *p2;
    int retval;
    mrb_int len, len1, len2;
    char buf1[8], buf2[8];

    p1 = sym2name_len(mrb, sym1, buf1, &len1);
    p2 = sym2name_len(mrb, sym2, buf2, &len2);
    len = lesser(len1, len2);
    retval = memcmp(p1, p2, len);
    if (retval == 0) {
      if (len1 == len2) return mrb_fixnum_value(0);
      if (len1 > len2)  return mrb_fixnum_value(1);
      return mrb_fixnum_value(-1);
    }
    if (retval > 0) return mrb_fixnum_value(1);
    return mrb_fixnum_value(-1);
  }
}
#undef lesser

/* ---------------------------*/
#ifndef MRB_NO_PRESYM
#define SYMBOL_ROM_MT_SIZE 6
static struct {
  union mt_ptr vals[SYMBOL_ROM_MT_SIZE];
  mrb_sym keys[SYMBOL_ROM_MT_SIZE];
} symbol_rom_data = {
  .vals = {
    { .func = sym_to_s },
    { .func = sym_name },
    { .func = mrb_obj_itself },
    { .func = sym_inspect },
    { .func = sym_cmp },
    { .func = mrb_obj_equal_m },
  },
  .keys = {
    MT_KEY(MRB_SYM(to_s),    MT_FUNC|MT_NOARG|MT_PUBLIC),
    MT_KEY(MRB_SYM(name),    MT_FUNC|MT_NOARG|MT_PUBLIC),
    MT_KEY(MRB_SYM(to_sym),  MT_FUNC|MT_NOARG|MT_PUBLIC),
    MT_KEY(MRB_SYM(inspect), MT_FUNC|MT_NOARG|MT_PUBLIC),
    MT_KEY(MRB_OPSYM(cmp),   MT_FUNC|MT_PUBLIC),
    MT_KEY(MRB_OPSYM(eq),    MT_FUNC|MT_PUBLIC),
  }
};
static mt_tbl symbol_rom_mt = {
  SYMBOL_ROM_MT_SIZE, SYMBOL_ROM_MT_SIZE,
  (union mt_ptr*)&symbol_rom_data, NULL
};
#endif /* !MRB_NO_PRESYM */

void
mrb_init_symbol(mrb_state *mrb)
{
  struct RClass *sym;

  mrb->symbol_class = sym = mrb_define_class_id(mrb, MRB_SYM(Symbol), mrb->object_class);  /* 15.2.11 */
  MRB_SET_INSTANCE_TT(sym, MRB_TT_SYMBOL);
  mrb_undef_class_method_id(mrb,  sym, MRB_SYM(new));

#ifndef MRB_NO_PRESYM
  mrb_mt_init_rom(sym, &symbol_rom_mt);
#else
  mrb_define_method_id(mrb, sym, MRB_SYM(to_s),    sym_to_s,    MRB_ARGS_NONE());          /* 15.2.11.3.3 */
  mrb_define_method_id(mrb, sym, MRB_SYM(name),    sym_name,    MRB_ARGS_NONE());
  mrb_define_method_id(mrb, sym, MRB_SYM(to_sym),  mrb_obj_itself,  MRB_ARGS_NONE());      /* 15.2.11.3.4 */
  mrb_define_method_id(mrb, sym, MRB_SYM(inspect), sym_inspect, MRB_ARGS_NONE());          /* 15.2.11.3.5(x) */
  mrb_define_method_id(mrb, sym, MRB_OPSYM(cmp),   sym_cmp,     MRB_ARGS_REQ(1));
  mrb_define_method_id(mrb, sym, MRB_OPSYM(eq),    mrb_obj_equal_m,      MRB_ARGS_REQ(1));
#endif
}