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more direct way to fill sign-extension extra bytes when packing 

integers with sizes larger than lua_Integer + added comments
This commit is contained in:
Roberto Ierusalimschy 2014-11-05 16:50:29 -02:00
parent 720c68dabb
commit ad73e5156e
1 changed files with 29 additions and 13 deletions
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42
lstrlib.c
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@ -1,5 +1,5 @@
/*
** $Id: lstrlib.c,v 1.212 2014/11/02 19:19:04 roberto Exp roberto $
** $Id: lstrlib.c,v 1.213 2014/11/04 14:34:43 roberto Exp roberto $
** Standard library for string operations and pattern-matching
** See Copyright Notice in lua.h
*/
@ -966,9 +966,6 @@ static int str_format (lua_State *L) {
/* size of a lua_Integer */
#define SZINT ((int)sizeof(lua_Integer))
/* mask for all ones in last byte in a lua Integer */
#define HIGHERBYTE ((lua_Unsigned)MC << (NB * (SZINT - 1)))
/* dummy union to get native endianness */
static const union {
@ -1049,7 +1046,8 @@ static int getnum (const char **fmt, int df) {
static int getnumlimit (Header *h, const char **fmt, int df) {
int sz = getnum(fmt, df);
if (sz > MAXINTSIZE || sz <= 0)
luaL_error(h->L, "integral size (%d) out of limits [1,%d]", sz, MAXINTSIZE);
luaL_error(h->L, "integral size (%d) out of limits [1,%d]",
sz, MAXINTSIZE);
return sz;
}
@ -1133,15 +1131,25 @@ static KOption getdetails (Header *h, size_t totalsize,
}
/*
** Pack integer 'n' with 'size' bytes and 'islittle' endianness.
** The final 'if' handles the case when 'size' is larger than
** the size of a Lua integer, correcting the extra sign-extension
** bytes if necessary (by default they would be zeros).
*/
static void packint (luaL_Buffer *b, lua_Unsigned n,
int islittle, int size, lua_Unsigned mask) {
int islittle, int size, int neg) {
char *buff = luaL_prepbuffsize(b, size);
int i;
for (i = 0; i < size - 1; i++) {
buff[islittle ? 0 : size - 1] = (char)(n & MC); /* first byte */
for (i = 1; i < size; i++) {
n >>= NB;
buff[islittle ? i : size - 1 - i] = (char)(n & MC);
n = (n >> NB) | mask;
}
buff[islittle ? i : size - 1 - i] = (char)(n & MC);
if (neg) { /* need sign extension (negative number)? */
for (i = SZINT; i < size; i++) /* correct extra bytes */
buff[islittle ? i : size - 1 - i] = (char)MC;
}
luaL_addsize(b, size); /* add result to buffer */
}
@ -1183,12 +1191,11 @@ static int str_pack (lua_State *L) {
switch (opt) {
case Kint: { /* signed integers */
lua_Integer n = luaL_checkinteger(L, arg);
lua_Unsigned mask = (n < 0) ? HIGHERBYTE : 0; /* sign extension */
if (size < SZINT) { /* need overflow check? */
lua_Integer lim = (lua_Integer)1 << ((size * NB) - 1);
luaL_argcheck(L, -lim <= n && n < lim, arg, "integer overflow");
}
packint(&b, (lua_Unsigned)n, h.islittle, size, mask);
packint(&b, (lua_Unsigned)n, h.islittle, size, (n < 0));
break;
}
case Kuint: { /* unsigned integers */
@ -1249,6 +1256,14 @@ static int str_pack (lua_State *L) {
}
/*
** Unpack an integer with 'size' bytes and 'islittle' endianness.
** If size is smaller than the size of a Lua integer and integer
** is signed, must do sign extension (propagating the sign to the
** higher bits); if size is larger than the size of a Lua integer,
** it must check the unread bytes to see whether they do not cause an
** overflow.
*/
static lua_Integer unpackint (lua_State *L, const char *str,
int islittle, int size, int issigned) {
lua_Unsigned res = 0;
@ -1264,11 +1279,12 @@ static lua_Integer unpackint (lua_State *L, const char *str,
res = ((res ^ mask) - mask); /* do sign extension */
}
}
else { /* must check unread bytes */
else if (size > SZINT) { /* must check unread bytes */
int mask = (!issigned || (lua_Integer)res >= 0) ? 0 : MC;
for (i = limit; i < size; i++) {
if ((unsigned char)str[islittle ? i : size - 1 - i] != mask)
luaL_error(L, "%d-bit integer does not fit into Lua Integer", size);
luaL_error(L, "%d-bit integer does not fit into Lua Integer",
size * NB);
}
}
return (lua_Integer)res;