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py: Implement integer overflow checking for * and << ops. 

If operation will overflow, a multi-precision integer is created.
This commit is contained in:
Damien George 2014-03-12 15:38:15 +00:00
parent bb4a43f35c
commit 9d68e9ccdd
5 changed files with 131 additions and 32 deletions
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6
py/obj.h
View File

@ -29,6 +29,8 @@ typedef struct _mp_obj_base_t mp_obj_base_t;
// - xxxx...xx00: a pointer to an mp_obj_base_t
// In SMALL_INT, next-to-highest bits is used as sign, so both must match for value in range
#define MP_SMALL_INT_MIN ((mp_small_int_t)(((machine_int_t)WORD_MSBIT_HIGH) >> 1))
#define MP_SMALL_INT_MAX ((mp_small_int_t)(~(MP_SMALL_INT_MIN)))
#define MP_OBJ_FITS_SMALL_INT(n) ((((n) ^ ((n) << 1)) & WORD_MSBIT_HIGH) == 0)
#define MP_OBJ_IS_SMALL_INT(o) ((((mp_small_int_t)(o)) & 1) != 0)
#define MP_OBJ_IS_QSTR(o) ((((mp_small_int_t)(o)) & 3) == 2)
@ -218,9 +220,7 @@ mp_obj_t mp_obj_new_cell(mp_obj_t obj);
mp_obj_t mp_obj_new_int(machine_int_t value);
mp_obj_t mp_obj_new_int_from_uint(machine_uint_t value);
mp_obj_t mp_obj_new_int_from_long_str(const char *s);
#if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
mp_obj_t mp_obj_new_int_from_ll(long long val);
#endif
mp_obj_t mp_obj_new_int_from_ll(long long val); // this must return a multi-precision integer object (or raise an overflow exception)
mp_obj_t mp_obj_new_str(const byte* data, uint len, bool make_qstr_if_not_already);
mp_obj_t mp_obj_new_bytes(const byte* data, uint len);
#if MICROPY_ENABLE_FLOAT

2
py/objfloat.c
View File

@ -17,8 +17,6 @@
#include "formatfloat.h"
#endif
mp_obj_t mp_obj_new_float(mp_float_t value);
STATIC void float_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t o_in, mp_print_kind_t kind) {
mp_obj_float_t *o = o_in;
#if MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_FLOAT

6
py/objint.c
View File

@ -71,6 +71,12 @@ mp_obj_t mp_obj_new_int_from_long_str(const char *s) {
return mp_const_none;
}
// This is called when an integer larger than a SMALL_INT is needed (although val might still fit in a SMALL_INT)
mp_obj_t mp_obj_new_int_from_ll(long long val) {
nlr_jump(mp_obj_new_exception_msg(&mp_type_OverflowError, "small int overflow"));
return mp_const_none;
}
mp_obj_t mp_obj_new_int_from_uint(machine_uint_t value) {
// SMALL_INT accepts only signed numbers, of one bit less size
// then word size, which totals 2 bits less for unsigned numbers.

2
py/objint_mpz.c
View File

@ -161,7 +161,7 @@ mp_obj_t mp_obj_new_int(machine_int_t value) {
mp_obj_t mp_obj_new_int_from_ll(long long val) {
mp_obj_int_t *o = mp_obj_int_new_mpz();
mpz_set_from_int(&o->mpz, val);
mpz_set_from_ll(&o->mpz, val);
return o;
}

147
py/runtime.c
View File

@ -455,16 +455,23 @@ mp_obj_t rt_unary_op(int op, mp_obj_t arg) {
if (MP_OBJ_IS_SMALL_INT(arg)) {
mp_small_int_t val = MP_OBJ_SMALL_INT_VALUE(arg);
switch (op) {
case RT_UNARY_OP_BOOL: return MP_BOOL(val != 0);
case RT_UNARY_OP_POSITIVE: break;
case RT_UNARY_OP_NEGATIVE: val = -val; break;
case RT_UNARY_OP_INVERT: val = ~val; break;
default: assert(0); val = 0;
case RT_UNARY_OP_BOOL:
return MP_BOOL(val != 0);
case RT_UNARY_OP_POSITIVE:
return arg;
case RT_UNARY_OP_NEGATIVE:
// check for overflow
if (val == MP_SMALL_INT_MIN) {
return mp_obj_new_int(-val);
} else {
return MP_OBJ_NEW_SMALL_INT(-val);
}
case RT_UNARY_OP_INVERT:
return MP_OBJ_NEW_SMALL_INT(~val);
default:
assert(0);
return arg;
}
if (MP_OBJ_FITS_SMALL_INT(val)) {
return MP_OBJ_NEW_SMALL_INT(val);
}
return mp_obj_new_int(val);
} else {
mp_obj_type_t *type = mp_obj_get_type(arg);
if (type->unary_op != NULL) {
@ -532,6 +539,15 @@ mp_obj_t rt_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
mp_small_int_t lhs_val = MP_OBJ_SMALL_INT_VALUE(lhs);
if (MP_OBJ_IS_SMALL_INT(rhs)) {
mp_small_int_t rhs_val = MP_OBJ_SMALL_INT_VALUE(rhs);
// This is a binary operation: lhs_val op rhs_val
// We need to be careful to handle overflow; see CERT INT32-C
// Operations that can overflow:
// + result always fits in machine_int_t, then handled by SMALL_INT check
// - result always fits in machine_int_t, then handled by SMALL_INT check
// * checked explicitly
// / if lhs=MIN and rhs=-1; result always fits in machine_int_t, then handled by SMALL_INT check
// % if lhs=MIN and rhs=-1; result always fits in machine_int_t, then handled by SMALL_INT check
// << checked explicitly
switch (op) {
case RT_BINARY_OP_OR:
case RT_BINARY_OP_INPLACE_OR: lhs_val |= rhs_val; break;
@ -540,41 +556,117 @@ mp_obj_t rt_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
case RT_BINARY_OP_AND:
case RT_BINARY_OP_INPLACE_AND: lhs_val &= rhs_val; break;
case RT_BINARY_OP_LSHIFT:
case RT_BINARY_OP_INPLACE_LSHIFT: lhs_val <<= rhs_val; break;
case RT_BINARY_OP_INPLACE_LSHIFT: {
if (rhs_val < 0) {
// negative shift not allowed
nlr_jump(mp_obj_new_exception_msg(&mp_type_ValueError, "negative shift count"));
} else if (rhs_val >= BITS_PER_WORD || lhs_val > (MP_SMALL_INT_MAX >> rhs_val) || lhs_val < (MP_SMALL_INT_MIN >> rhs_val)) {
// left-shift will overflow, so use higher precision integer
lhs = mp_obj_new_int_from_ll(lhs_val);
goto generic_binary_op;
} else {
// use standard precision
lhs_val <<= rhs_val;
}
break;
}
case RT_BINARY_OP_RSHIFT:
case RT_BINARY_OP_INPLACE_RSHIFT: lhs_val >>= rhs_val; break;
case RT_BINARY_OP_INPLACE_RSHIFT:
if (rhs_val < 0) {
// negative shift not allowed
nlr_jump(mp_obj_new_exception_msg(&mp_type_ValueError, "negative shift count"));
} else {
// standard precision is enough for right-shift
lhs_val >>= rhs_val;
}
break;
case RT_BINARY_OP_ADD:
case RT_BINARY_OP_INPLACE_ADD: lhs_val += rhs_val; break;
case RT_BINARY_OP_SUBTRACT:
case RT_BINARY_OP_INPLACE_SUBTRACT: lhs_val -= rhs_val; break;
case RT_BINARY_OP_MULTIPLY:
case RT_BINARY_OP_INPLACE_MULTIPLY: lhs_val *= rhs_val; break;
case RT_BINARY_OP_INPLACE_MULTIPLY: {
// If long long type exists and is larger than machine_int_t, then
// we can use the following code to perform overflow-checked multiplication.
// Otherwise (eg in x64 case) we must use the branching code below.
#if 0
// compute result using long long precision
long long res = (long long)lhs_val * (long long)rhs_val;
if (res > MP_SMALL_INT_MAX || res < MP_SMALL_INT_MIN) {
// result overflowed SMALL_INT, so return higher precision integer
return mp_obj_new_int_from_ll(res);
} else {
// use standard precision
lhs_val = (mp_small_int_t)res;
}
#endif
if (lhs_val > 0) { // lhs_val is positive
if (rhs_val > 0) { // lhs_val and rhs_val are positive
if (lhs_val > (MP_SMALL_INT_MAX / rhs_val)) {
goto mul_overflow;
}
} else { // lhs_val positive, rhs_val nonpositive
if (rhs_val < (MP_SMALL_INT_MIN / lhs_val)) {
goto mul_overflow;
}
} // lhs_val positive, rhs_val nonpositive
} else { // lhs_val is nonpositive
if (rhs_val > 0) { // lhs_val is nonpositive, rhs_val is positive
if (lhs_val < (MP_SMALL_INT_MIN / rhs_val)) {
goto mul_overflow;
}
} else { // lhs_val and rhs_val are nonpositive
if (lhs_val != 0 && rhs_val < (MP_SMALL_INT_MAX / lhs_val)) {
goto mul_overflow;
}
} // End if lhs_val and rhs_val are nonpositive
} // End if lhs_val is nonpositive
// use standard precision
return MP_OBJ_NEW_SMALL_INT(lhs_val * rhs_val);
mul_overflow:
// use higher precision
lhs = mp_obj_new_int_from_ll(lhs_val);
goto generic_binary_op;
break;
}
case RT_BINARY_OP_FLOOR_DIVIDE:
case RT_BINARY_OP_INPLACE_FLOOR_DIVIDE: lhs_val /= rhs_val; break;
#if MICROPY_ENABLE_FLOAT
#if MICROPY_ENABLE_FLOAT
case RT_BINARY_OP_TRUE_DIVIDE:
case RT_BINARY_OP_INPLACE_TRUE_DIVIDE: return mp_obj_new_float((mp_float_t)lhs_val / (mp_float_t)rhs_val);
#endif
#endif
// TODO implement modulo as specified by Python
case RT_BINARY_OP_MODULO:
case RT_BINARY_OP_INPLACE_MODULO: lhs_val %= rhs_val; break;
// TODO check for negative power, and overflow
case RT_BINARY_OP_POWER:
case RT_BINARY_OP_INPLACE_POWER:
{
int ans = 1;
while (rhs_val > 0) {
if (rhs_val & 1) {
ans *= lhs_val;
if (rhs_val < 0) {
#if MICROPY_ENABLE_FLOAT
lhs = mp_obj_new_float(lhs_val);
goto generic_binary_op;
#else
nlr_jump(mp_obj_new_exception_msg(&mp_type_ValueError, "negative power with no float support"));
#endif
} else {
// TODO check for overflow
machine_int_t ans = 1;
while (rhs_val > 0) {
if (rhs_val & 1) {
ans *= lhs_val;
}
lhs_val *= lhs_val;
rhs_val /= 2;
}
lhs_val *= lhs_val;
rhs_val /= 2;
lhs_val = ans;
}
lhs_val = ans;
break;
}
case RT_BINARY_OP_LESS: return MP_BOOL(lhs_val < rhs_val); break;
case RT_BINARY_OP_MORE: return MP_BOOL(lhs_val > rhs_val); break;
case RT_BINARY_OP_LESS_EQUAL: return MP_BOOL(lhs_val <= rhs_val); break;
@ -585,8 +677,9 @@ mp_obj_t rt_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
// TODO: We just should make mp_obj_new_int() inline and use that
if (MP_OBJ_FITS_SMALL_INT(lhs_val)) {
return MP_OBJ_NEW_SMALL_INT(lhs_val);
} else {
return mp_obj_new_int(lhs_val);
}
return mp_obj_new_int(lhs_val);
#if MICROPY_ENABLE_FLOAT
} else if (MP_OBJ_IS_TYPE(rhs, &mp_type_float)) {
return mp_obj_float_binary_op(op, lhs_val, rhs);
@ -628,7 +721,9 @@ mp_obj_t rt_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
}
// generic binary_op supplied by type
mp_obj_type_t *type = mp_obj_get_type(lhs);
mp_obj_type_t *type;
generic_binary_op:
type = mp_obj_get_type(lhs);
if (type->binary_op != NULL) {
mp_obj_t result = type->binary_op(op, lhs, rhs);
if (result != MP_OBJ_NULL) {