From 26be27459b11feabed52cf40aaa76f86c7edc977 Mon Sep 17 00:00:00 2001 From: Roberto Ierusalimschy Date: Fri, 23 Sep 2022 11:08:10 -0300 Subject: Negation in constant folding of '>>' may overflow --- lobject.c | 2 +- lvm.c | 4 +--- lvm.h | 5 +++++ testes/bitwise.lua | 12 ++++++++++++ 4 files changed, 19 insertions(+), 4 deletions(-) diff --git a/lobject.c b/lobject.c index a2c00609..03e2798c 100644 --- a/lobject.c +++ b/lobject.c @@ -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; diff --git a/lvm.c b/lvm.c index 614df055..73a19ba9 100644 --- a/lvm.c +++ b/lvm.c @@ -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; diff --git a/lvm.h b/lvm.h index 1bc16f3a..dba1ad27 100644 --- a/lvm.h +++ b/lvm.h @@ -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); diff --git a/testes/bitwise.lua b/testes/bitwise.lua index 9509f7f0..dd0a1a9a 100644 --- a/testes/bitwise.lua +++ b/testes/bitwise.lua @@ -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 -- cgit v1.2.1