New implementation for 'luaL_addvalue'

The function 'luaL_addvalue' (from the buffer system) was rewritten so that it does not change the position of the box (if present) in the stack.
author: Roberto Ierusalimschy <roberto@inf.puc-rio.br> 2018-11-09 17:03:52 -0200
committer: Roberto Ierusalimschy <roberto@inf.puc-rio.br> 2018-11-09 17:03:52 -0200
commit: 9eafe9c053ef17a0980ab32082bf229bd58e963b (patch)
tree: ce5af4e070b71c714420817c367cc2b16393a112
parent: 7f6f70853c8a2730fca2e95d5968ad52cf470bda (diff)
download: lua-9eafe9c053ef17a0980ab32082bf229bd58e963b.tar.gz
lua-9eafe9c053ef17a0980ab32082bf229bd58e963b.tar.bz2
lua-9eafe9c053ef17a0980ab32082bf229bd58e963b.zip
1 files changed, 59 insertions, 22 deletions
diff --git a/lauxlib.c b/lauxlib.c
index 78dfb4e9..68842a98 100644
--- a/lauxlib.c
+++ b/lauxlib.c
@@ -27,6 +27,12 @@
 #include "lauxlib.h"
+#if !defined(MAX_SIZET)
+/* maximum value for size_t */
+#define MAX_SIZET       ((size_t)(~(size_t)0))
+#endif
 /*
 ** {======================================================
 ** Traceback
@@ -501,34 +507,56 @@ static void *newbox (lua_State *L, size_t newsize) {
 /*
-** returns a pointer to a free area with at least 'sz' bytes
+** Compute new size for buffer 'B', enough to accommodate extra 'sz'
+** bytes.
 */
-LUALIB_API char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz) {
+static size_t newbuffsize (luaL_Buffer *B, size_t sz) {
-  lua_State *L = B->L;
+  size_t newsize = B->size * 2;  /* double buffer size */
-  if (B->size - B->n < sz) {  /* not enough space? */
+  if (MAX_SIZET - sz < B->n)  /* overflow in (B->n + sz)? */
+    return luaL_error(B->L, "buffer too large");
+  if (newsize < B->n + sz)  /* double is not big enough? */
+    newsize = B->n + sz;
+  return newsize;
+}
+/*
+** Returns a pointer to a free area with at least 'sz' bytes in buffer
+** 'B'. 'boxidx' is the position in the stack where the buffer's box is
+** or should be.
+*/
+static char *prepbuffsize (luaL_Buffer *B, size_t sz, int boxidx) {
+  if (B->size - B->n >= sz)  /* enough space? */
+    return B->b + B->n;
+  else {
+    lua_State *L = B->L;
    char *newbuff;
-    size_t newsize = B->size * 2;  /* double buffer size */
+    size_t newsize = newbuffsize(B, sz);
-    if (newsize - B->n < sz)  /* not big enough? */
-      newsize = B->n + sz;
-    if (newsize < B->n || newsize - B->n < sz)
-      luaL_error(L, "buffer too large");
    /* create larger buffer */
-    if (buffonstack(B))
+    if (buffonstack(B))  /* buffer already has a box? */
-      newbuff = (char *)resizebox(L, -1, newsize);
+      newbuff = (char *)resizebox(L, boxidx, newsize);  /* resize it */
-    else {  /* no buffer yet */
+    else {  /* no box yet */
-      newbuff = (char *)newbox(L, newsize);
+      newbuff = (char *)newbox(L, newsize);  /* create a new box */
      memcpy(newbuff, B->b, B->n * sizeof(char));  /* copy original content */
+      lua_insert(L, boxidx);  /* move box to its intended position */
    }
    B->b = newbuff;
    B->size = newsize;
+    return newbuff + B->n;
  }
-  return &B->b[B->n];
+}
+/*
+** returns a pointer to a free area with at least 'sz' bytes
+*/
+LUALIB_API char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz) {
+  return prepbuffsize(B, sz, -1);
 }
 LUALIB_API void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l) {
  if (l > 0) {  /* avoid 'memcpy' when 's' can be NULL */
-    char *b = luaL_prepbuffsize(B, l);
+    char *b = prepbuffsize(B, l, -1);
    memcpy(b, s, l * sizeof(char));
    luaL_addsize(B, l);
  }
@@ -556,14 +584,23 @@ LUALIB_API void luaL_pushresultsize (luaL_Buffer *B, size_t sz) {
 }
+/*
+** 'luaL_addvalue' is the only function in the Buffer system where the
+** box (if existent) is not on the top of the stack. So, instead of
+** calling 'luaL_addlstring', it replicates the code using -2 as the
+** last argument to 'prepbuffsize', signaling that the box is (or will
+** be) bellow the string being added to the buffer. (Box creation can
+** trigger an emergency GC, so we should not remove the string from the
+** stack before we have the space guaranteed.)
+*/
 LUALIB_API void luaL_addvalue (luaL_Buffer *B) {
  lua_State *L = B->L;
-  size_t l;
+  size_t len;
-  const char *s = lua_tolstring(L, -1, &l);
+  const char *s = lua_tolstring(L, -1, &len);
-  if (buffonstack(B))
+  char *b = prepbuffsize(B, len, -2);
-    lua_insert(L, -2);  /* put value below buffer */
+  memcpy(b, s, len * sizeof(char));
-  luaL_addlstring(B, s, l);
+  luaL_addsize(B, len);
-  lua_remove(L, (buffonstack(B)) ? -2 : -1);  /* remove value */
+  lua_pop(L, 1);  /* pop string */
 }
@@ -577,7 +614,7 @@ LUALIB_API void luaL_buffinit (lua_State *L, luaL_Buffer *B) {
 LUALIB_API char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz) {
  luaL_buffinit(L, B);
-  return luaL_prepbuffsize(B, sz);
+  return prepbuffsize(B, sz, -1);
 }
 /* }====================================================== */
author	Roberto Ierusalimschy <roberto@inf.puc-rio.br>	2018-11-09 17:03:52 -0200
committer	Roberto Ierusalimschy <roberto@inf.puc-rio.br>	2018-11-09 17:03:52 -0200
commit	9eafe9c053ef17a0980ab32082bf229bd58e963b (patch)
tree	ce5af4e070b71c714420817c367cc2b16393a112
parent	7f6f70853c8a2730fca2e95d5968ad52cf470bda (diff)
download	lua-9eafe9c053ef17a0980ab32082bf229bd58e963b.tar.gz lua-9eafe9c053ef17a0980ab32082bf229bd58e963b.tar.bz2 lua-9eafe9c053ef17a0980ab32082bf229bd58e963b.zip