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Negation in constant folding of '>>' may overflow

This commit is contained in:
Roberto Ierusalimschy 2022-09-23 11:08:10 -03:00
parent cfbe378f90
commit 26be27459b
4 changed files with 19 additions and 4 deletions
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2
lobject.c
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@ -62,7 +62,7 @@ static lua_Integer intarith (lua_State *L, int op, lua_Integer v1,
case LUA_OPBOR: return intop(|, v1, v2);
case LUA_OPBXOR: return intop(^, v1, v2);
case LUA_OPSHL: return luaV_shiftl(v1, v2);
case LUA_OPSHR: return luaV_shiftl(v1, -v2);
case LUA_OPSHR: return luaV_shiftr(v1, v2);
case LUA_OPUNM: return intop(-, 0, v1);
case LUA_OPBNOT: return intop(^, ~l_castS2U(0), v1);
default: lua_assert(0); return 0;

4
lvm.c
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@ -765,12 +765,10 @@ lua_Number luaV_modf (lua_State *L, lua_Number m, lua_Number n) {
/* number of bits in an integer */
#define NBITS cast_int(sizeof(lua_Integer) * CHAR_BIT)
/*
** Shift left operation. (Shift right just negates 'y'.)
*/
#define luaV_shiftr(x,y) luaV_shiftl(x,intop(-, 0, y))
lua_Integer luaV_shiftl (lua_Integer x, lua_Integer y) {
if (y < 0) { /* shift right? */
if (y <= -NBITS) return 0;

5
lvm.h
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@ -110,6 +110,11 @@ typedef enum {
luaC_barrierback(L, gcvalue(t), v); }
/*
** Shift right is the same as shift left with a negative 'y'
*/
#define luaV_shiftr(x,y) luaV_shiftl(x,intop(-, 0, y))
LUAI_FUNC int luaV_equalobj (lua_State *L, const TValue *t1, const TValue *t2);

12
testes/bitwise.lua
View File

@ -38,6 +38,18 @@ d = d << 32
assert(a | b ~ c & d == 0xF4000000 << 32)
assert(~~a == a and ~a == -1 ~ a and -d == ~d + 1)
do -- constant folding
local code = string.format("return -1 >> %d", math.maxinteger)
assert(load(code)() == 0)
local code = string.format("return -1 >> %d", math.mininteger)
assert(load(code)() == 0)
local code = string.format("return -1 << %d", math.maxinteger)
assert(load(code)() == 0)
local code = string.format("return -1 << %d", math.mininteger)
assert(load(code)() == 0)
end
assert(-1 >> 1 == (1 << (numbits - 1)) - 1 and 1 << 31 == 0x80000000)
assert(-1 >> (numbits - 1) == 1)
assert(-1 >> numbits == 0 and