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longobject.c
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longobject.c
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/* Long (arbitrary precision) integer object implementation */
/* XXX The functional organization of this file is terrible */
#include "Python.h"
#include "longintrepr.h"
#include <float.h>
#include <ctype.h>
#include <stddef.h>
#include "clinic/longobject.c.h"
/*[clinic input]
class int "PyObject *" "&PyLong_Type"
[clinic start generated code]*/
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=ec0275e3422a36e3]*/
#ifndef NSMALLPOSINTS
#define NSMALLPOSINTS 257
#endif
#ifndef NSMALLNEGINTS
#define NSMALLNEGINTS 5
#endif
_Py_IDENTIFIER(little);
_Py_IDENTIFIER(big);
/* convert a PyLong of size 1, 0 or -1 to an sdigit */
#define MEDIUM_VALUE(x) (assert(-1 <= Py_SIZE(x) && Py_SIZE(x) <= 1), \
Py_SIZE(x) < 0 ? -(sdigit)(x)->ob_digit[0] : \
(Py_SIZE(x) == 0 ? (sdigit)0 : \
(sdigit)(x)->ob_digit[0]))
PyObject *_PyLong_Zero = NULL;
PyObject *_PyLong_One = NULL;
#if NSMALLNEGINTS + NSMALLPOSINTS > 0
/* Small integers are preallocated in this array so that they
can be shared.
The integers that are preallocated are those in the range
-NSMALLNEGINTS (inclusive) to NSMALLPOSINTS (not inclusive).
*/
static PyLongObject small_ints[NSMALLNEGINTS + NSMALLPOSINTS];
#ifdef COUNT_ALLOCS
Py_ssize_t quick_int_allocs, quick_neg_int_allocs;
#endif
static PyObject *
get_small_int(sdigit ival)
{
PyObject *v;
assert(-NSMALLNEGINTS <= ival && ival < NSMALLPOSINTS);
v = (PyObject *)&small_ints[ival + NSMALLNEGINTS];
Py_INCREF(v);
#ifdef COUNT_ALLOCS
if (ival >= 0)
quick_int_allocs++;
else
quick_neg_int_allocs++;
#endif
return v;
}
#define CHECK_SMALL_INT(ival) \
do if (-NSMALLNEGINTS <= ival && ival < NSMALLPOSINTS) { \
return get_small_int((sdigit)ival); \
} while(0)
static PyLongObject *
maybe_small_long(PyLongObject *v)
{
if (v && Py_ABS(Py_SIZE(v)) <= 1) {
sdigit ival = MEDIUM_VALUE(v);
if (-NSMALLNEGINTS <= ival && ival < NSMALLPOSINTS) {
Py_DECREF(v);
return (PyLongObject *)get_small_int(ival);
}
}
return v;
}
#else
#define CHECK_SMALL_INT(ival)
#define maybe_small_long(val) (val)
#endif
/* If a freshly-allocated int is already shared, it must
be a small integer, so negating it must go to PyLong_FromLong */
Py_LOCAL_INLINE(void)
_PyLong_Negate(PyLongObject **x_p)
{
PyLongObject *x;
x = (PyLongObject *)*x_p;
if (Py_REFCNT(x) == 1) {
Py_SIZE(x) = -Py_SIZE(x);
return;
}
*x_p = (PyLongObject *)PyLong_FromLong(-MEDIUM_VALUE(x));
Py_DECREF(x);
}
/* For int multiplication, use the O(N**2) school algorithm unless
* both operands contain more than KARATSUBA_CUTOFF digits (this
* being an internal Python int digit, in base BASE).
*/
#define KARATSUBA_CUTOFF 70
#define KARATSUBA_SQUARE_CUTOFF (2 * KARATSUBA_CUTOFF)
/* For exponentiation, use the binary left-to-right algorithm
* unless the exponent contains more than FIVEARY_CUTOFF digits.
* In that case, do 5 bits at a time. The potential drawback is that
* a table of 2**5 intermediate results is computed.
*/
#define FIVEARY_CUTOFF 8
#define SIGCHECK(PyTryBlock) \
do { \
if (PyErr_CheckSignals()) PyTryBlock \
} while(0)
/* Normalize (remove leading zeros from) an int object.
Doesn't attempt to free the storage--in most cases, due to the nature
of the algorithms used, this could save at most be one word anyway. */
static PyLongObject *
long_normalize(PyLongObject *v)
{
Py_ssize_t j = Py_ABS(Py_SIZE(v));
Py_ssize_t i = j;
while (i > 0 && v->ob_digit[i-1] == 0)
--i;
if (i != j)
Py_SIZE(v) = (Py_SIZE(v) < 0) ? -(i) : i;
return v;
}
/* _PyLong_FromNbInt: Convert the given object to a PyLongObject
using the nb_int slot, if available. Raise TypeError if either the
nb_int slot is not available or the result of the call to nb_int
returns something not of type int.
*/
PyLongObject *
_PyLong_FromNbInt(PyObject *integral)
{
PyNumberMethods *nb;
PyObject *result;
/* Fast path for the case that we already have an int. */
if (PyLong_CheckExact(integral)) {
Py_INCREF(integral);
return (PyLongObject *)integral;
}
nb = Py_TYPE(integral)->tp_as_number;
if (nb == NULL || nb->nb_int == NULL) {
PyErr_Format(PyExc_TypeError,
"an integer is required (got type %.200s)",
Py_TYPE(integral)->tp_name);
return NULL;
}
/* Convert using the nb_int slot, which should return something
of exact type int. */
result = nb->nb_int(integral);
if (!result || PyLong_CheckExact(result))
return (PyLongObject *)result;
if (!PyLong_Check(result)) {
PyErr_Format(PyExc_TypeError,
"__int__ returned non-int (type %.200s)",
result->ob_type->tp_name);
Py_DECREF(result);
return NULL;
}
/* Issue #17576: warn if 'result' not of exact type int. */
if (PyErr_WarnFormat(PyExc_DeprecationWarning, 1,
"__int__ returned non-int (type %.200s). "
"The ability to return an instance of a strict subclass of int "
"is deprecated, and may be removed in a future version of Python.",
result->ob_type->tp_name)) {
Py_DECREF(result);
return NULL;
}
return (PyLongObject *)result;
}
/* Allocate a new int object with size digits.
Return NULL and set exception if we run out of memory. */
#define MAX_LONG_DIGITS \
((PY_SSIZE_T_MAX - offsetof(PyLongObject, ob_digit))/sizeof(digit))
PyLongObject *
_PyLong_New(Py_ssize_t size)
{
PyLongObject *result;
/* Number of bytes needed is: offsetof(PyLongObject, ob_digit) +
sizeof(digit)*size. Previous incarnations of this code used
sizeof(PyVarObject) instead of the offsetof, but this risks being
incorrect in the presence of padding between the PyVarObject header
and the digits. */
if (size > (Py_ssize_t)MAX_LONG_DIGITS) {
PyErr_SetString(PyExc_OverflowError,
"too many digits in integer");
return NULL;
}
result = PyObject_MALLOC(offsetof(PyLongObject, ob_digit) +
size*sizeof(digit));
if (!result) {
PyErr_NoMemory();
return NULL;
}
return (PyLongObject*)PyObject_INIT_VAR(result, &PyLong_Type, size);
}
PyObject *
_PyLong_Copy(PyLongObject *src)
{
PyLongObject *result;
Py_ssize_t i;
assert(src != NULL);
i = Py_SIZE(src);
if (i < 0)
i = -(i);
if (i < 2) {
sdigit ival = MEDIUM_VALUE(src);
CHECK_SMALL_INT(ival);
}
result = _PyLong_New(i);
if (result != NULL) {
Py_SIZE(result) = Py_SIZE(src);
while (--i >= 0)
result->ob_digit[i] = src->ob_digit[i];
}
return (PyObject *)result;
}
/* Create a new int object from a C long int */
PyObject *
PyLong_FromLong(long ival)
{
PyLongObject *v;
unsigned long abs_ival;
unsigned long t; /* unsigned so >> doesn't propagate sign bit */
int ndigits = 0;
int sign;
CHECK_SMALL_INT(ival);
if (ival < 0) {
/* negate: can't write this as abs_ival = -ival since that
invokes undefined behaviour when ival is LONG_MIN */
abs_ival = 0U-(unsigned long)ival;
sign = -1;
}
else {
abs_ival = (unsigned long)ival;
sign = ival == 0 ? 0 : 1;
}
/* Fast path for single-digit ints */
if (!(abs_ival >> PyLong_SHIFT)) {
v = _PyLong_New(1);
if (v) {
Py_SIZE(v) = sign;
v->ob_digit[0] = Py_SAFE_DOWNCAST(
abs_ival, unsigned long, digit);
}
return (PyObject*)v;
}
#if PyLong_SHIFT==15
/* 2 digits */
if (!(abs_ival >> 2*PyLong_SHIFT)) {
v = _PyLong_New(2);
if (v) {
Py_SIZE(v) = 2*sign;
v->ob_digit[0] = Py_SAFE_DOWNCAST(
abs_ival & PyLong_MASK, unsigned long, digit);
v->ob_digit[1] = Py_SAFE_DOWNCAST(
abs_ival >> PyLong_SHIFT, unsigned long, digit);
}
return (PyObject*)v;
}
#endif
/* Larger numbers: loop to determine number of digits */
t = abs_ival;
while (t) {
++ndigits;
t >>= PyLong_SHIFT;
}
v = _PyLong_New(ndigits);
if (v != NULL) {
digit *p = v->ob_digit;
Py_SIZE(v) = ndigits*sign;
t = abs_ival;
while (t) {
*p++ = Py_SAFE_DOWNCAST(
t & PyLong_MASK, unsigned long, digit);
t >>= PyLong_SHIFT;
}
}
return (PyObject *)v;
}
/* Create a new int object from a C unsigned long int */
PyObject *
PyLong_FromUnsignedLong(unsigned long ival)
{
PyLongObject *v;
unsigned long t;
int ndigits = 0;
if (ival < PyLong_BASE)
return PyLong_FromLong(ival);
/* Count the number of Python digits. */
t = ival;
while (t) {
++ndigits;
t >>= PyLong_SHIFT;
}
v = _PyLong_New(ndigits);
if (v != NULL) {
digit *p = v->ob_digit;
while (ival) {
*p++ = (digit)(ival & PyLong_MASK);
ival >>= PyLong_SHIFT;
}
}
return (PyObject *)v;
}
/* Create a new int object from a C double */
PyObject *
PyLong_FromDouble(double dval)
{
PyLongObject *v;
double frac;
int i, ndig, expo, neg;
neg = 0;
if (Py_IS_INFINITY(dval)) {
PyErr_SetString(PyExc_OverflowError,
"cannot convert float infinity to integer");
return NULL;
}
if (Py_IS_NAN(dval)) {
PyErr_SetString(PyExc_ValueError,
"cannot convert float NaN to integer");
return NULL;
}
if (dval < 0.0) {
neg = 1;
dval = -dval;
}
frac = frexp(dval, &expo); /* dval = frac*2**expo; 0.0 <= frac < 1.0 */
if (expo <= 0)
return PyLong_FromLong(0L);
ndig = (expo-1) / PyLong_SHIFT + 1; /* Number of 'digits' in result */
v = _PyLong_New(ndig);
if (v == NULL)
return NULL;
frac = ldexp(frac, (expo-1) % PyLong_SHIFT + 1);
for (i = ndig; --i >= 0; ) {
digit bits = (digit)frac;
v->ob_digit[i] = bits;
frac = frac - (double)bits;
frac = ldexp(frac, PyLong_SHIFT);
}
if (neg)
Py_SIZE(v) = -(Py_SIZE(v));
return (PyObject *)v;
}
/* Checking for overflow in PyLong_AsLong is a PITA since C doesn't define
* anything about what happens when a signed integer operation overflows,
* and some compilers think they're doing you a favor by being "clever"
* then. The bit pattern for the largest positive signed long is
* (unsigned long)LONG_MAX, and for the smallest negative signed long
* it is abs(LONG_MIN), which we could write -(unsigned long)LONG_MIN.
* However, some other compilers warn about applying unary minus to an
* unsigned operand. Hence the weird "0-".
*/
#define PY_ABS_LONG_MIN (0-(unsigned long)LONG_MIN)
#define PY_ABS_SSIZE_T_MIN (0-(size_t)PY_SSIZE_T_MIN)
/* Get a C long int from an int object or any object that has an __int__
method.
On overflow, return -1 and set *overflow to 1 or -1 depending on the sign of
the result. Otherwise *overflow is 0.
For other errors (e.g., TypeError), return -1 and set an error condition.
In this case *overflow will be 0.
*/
long
PyLong_AsLongAndOverflow(PyObject *vv, int *overflow)
{
/* This version by Tim Peters */
PyLongObject *v;
unsigned long x, prev;
long res;
Py_ssize_t i;
int sign;
int do_decref = 0; /* if nb_int was called */
*overflow = 0;
if (vv == NULL) {
PyErr_BadInternalCall();
return -1;
}
if (PyLong_Check(vv)) {
v = (PyLongObject *)vv;
}
else {
v = _PyLong_FromNbInt(vv);
if (v == NULL)
return -1;
do_decref = 1;
}
res = -1;
i = Py_SIZE(v);
switch (i) {
case -1:
res = -(sdigit)v->ob_digit[0];
break;
case 0:
res = 0;
break;
case 1:
res = v->ob_digit[0];
break;
default:
sign = 1;
x = 0;
if (i < 0) {
sign = -1;
i = -(i);
}
while (--i >= 0) {
prev = x;
x = (x << PyLong_SHIFT) | v->ob_digit[i];
if ((x >> PyLong_SHIFT) != prev) {
*overflow = sign;
goto exit;
}
}
/* Haven't lost any bits, but casting to long requires extra
* care (see comment above).
*/
if (x <= (unsigned long)LONG_MAX) {
res = (long)x * sign;
}
else if (sign < 0 && x == PY_ABS_LONG_MIN) {
res = LONG_MIN;
}
else {
*overflow = sign;
/* res is already set to -1 */
}
}
exit:
if (do_decref) {
Py_DECREF(v);
}
return res;
}
/* Get a C long int from an int object or any object that has an __int__
method. Return -1 and set an error if overflow occurs. */
long
PyLong_AsLong(PyObject *obj)
{
int overflow;
long result = PyLong_AsLongAndOverflow(obj, &overflow);
if (overflow) {
/* XXX: could be cute and give a different
message for overflow == -1 */
PyErr_SetString(PyExc_OverflowError,
"Python int too large to convert to C long");
}
return result;
}
/* Get a C int from an int object or any object that has an __int__
method. Return -1 and set an error if overflow occurs. */
int
_PyLong_AsInt(PyObject *obj)
{
int overflow;
long result = PyLong_AsLongAndOverflow(obj, &overflow);
if (overflow || result > INT_MAX || result < INT_MIN) {
/* XXX: could be cute and give a different
message for overflow == -1 */
PyErr_SetString(PyExc_OverflowError,
"Python int too large to convert to C int");
return -1;
}
return (int)result;
}
/* Get a Py_ssize_t from an int object.
Returns -1 and sets an error condition if overflow occurs. */
Py_ssize_t
PyLong_AsSsize_t(PyObject *vv) {
PyLongObject *v;
size_t x, prev;
Py_ssize_t i;
int sign;
if (vv == NULL) {
PyErr_BadInternalCall();
return -1;
}
if (!PyLong_Check(vv)) {
PyErr_SetString(PyExc_TypeError, "an integer is required");
return -1;
}
v = (PyLongObject *)vv;
i = Py_SIZE(v);
switch (i) {
case -1: return -(sdigit)v->ob_digit[0];
case 0: return 0;
case 1: return v->ob_digit[0];
}
sign = 1;
x = 0;
if (i < 0) {
sign = -1;
i = -(i);
}
while (--i >= 0) {
prev = x;
x = (x << PyLong_SHIFT) | v->ob_digit[i];
if ((x >> PyLong_SHIFT) != prev)
goto overflow;
}
/* Haven't lost any bits, but casting to a signed type requires
* extra care (see comment above).
*/
if (x <= (size_t)PY_SSIZE_T_MAX) {
return (Py_ssize_t)x * sign;
}
else if (sign < 0 && x == PY_ABS_SSIZE_T_MIN) {
return PY_SSIZE_T_MIN;
}
/* else overflow */
overflow:
PyErr_SetString(PyExc_OverflowError,
"Python int too large to convert to C ssize_t");
return -1;
}
/* Get a C unsigned long int from an int object.
Returns -1 and sets an error condition if overflow occurs. */
unsigned long
PyLong_AsUnsignedLong(PyObject *vv)
{
PyLongObject *v;
unsigned long x, prev;
Py_ssize_t i;
if (vv == NULL) {
PyErr_BadInternalCall();
return (unsigned long)-1;
}
if (!PyLong_Check(vv)) {
PyErr_SetString(PyExc_TypeError, "an integer is required");
return (unsigned long)-1;
}
v = (PyLongObject *)vv;
i = Py_SIZE(v);
x = 0;
if (i < 0) {
PyErr_SetString(PyExc_OverflowError,
"can't convert negative value to unsigned int");
return (unsigned long) -1;
}
switch (i) {
case 0: return 0;
case 1: return v->ob_digit[0];
}
while (--i >= 0) {
prev = x;
x = (x << PyLong_SHIFT) | v->ob_digit[i];
if ((x >> PyLong_SHIFT) != prev) {
PyErr_SetString(PyExc_OverflowError,
"Python int too large to convert "
"to C unsigned long");
return (unsigned long) -1;
}
}
return x;
}
/* Get a C size_t from an int object. Returns (size_t)-1 and sets
an error condition if overflow occurs. */
size_t
PyLong_AsSize_t(PyObject *vv)
{
PyLongObject *v;
size_t x, prev;
Py_ssize_t i;
if (vv == NULL) {
PyErr_BadInternalCall();
return (size_t) -1;
}
if (!PyLong_Check(vv)) {
PyErr_SetString(PyExc_TypeError, "an integer is required");
return (size_t)-1;
}
v = (PyLongObject *)vv;
i = Py_SIZE(v);
x = 0;
if (i < 0) {
PyErr_SetString(PyExc_OverflowError,
"can't convert negative value to size_t");
return (size_t) -1;
}
switch (i) {
case 0: return 0;
case 1: return v->ob_digit[0];
}
while (--i >= 0) {
prev = x;
x = (x << PyLong_SHIFT) | v->ob_digit[i];
if ((x >> PyLong_SHIFT) != prev) {
PyErr_SetString(PyExc_OverflowError,
"Python int too large to convert to C size_t");
return (size_t) -1;
}
}
return x;
}
/* Get a C unsigned long int from an int object, ignoring the high bits.
Returns -1 and sets an error condition if an error occurs. */
static unsigned long
_PyLong_AsUnsignedLongMask(PyObject *vv)
{
PyLongObject *v;
unsigned long x;
Py_ssize_t i;
int sign;
if (vv == NULL || !PyLong_Check(vv)) {
PyErr_BadInternalCall();
return (unsigned long) -1;
}
v = (PyLongObject *)vv;
i = Py_SIZE(v);
switch (i) {
case 0: return 0;
case 1: return v->ob_digit[0];
}
sign = 1;
x = 0;
if (i < 0) {
sign = -1;
i = -i;
}
while (--i >= 0) {
x = (x << PyLong_SHIFT) | v->ob_digit[i];
}
return x * sign;
}
unsigned long
PyLong_AsUnsignedLongMask(PyObject *op)
{
PyLongObject *lo;
unsigned long val;
if (op == NULL) {
PyErr_BadInternalCall();
return (unsigned long)-1;
}
if (PyLong_Check(op)) {
return _PyLong_AsUnsignedLongMask(op);
}
lo = _PyLong_FromNbInt(op);
if (lo == NULL)
return (unsigned long)-1;
val = _PyLong_AsUnsignedLongMask((PyObject *)lo);
Py_DECREF(lo);
return val;
}
int
_PyLong_Sign(PyObject *vv)
{
PyLongObject *v = (PyLongObject *)vv;
assert(v != NULL);
assert(PyLong_Check(v));
return Py_SIZE(v) == 0 ? 0 : (Py_SIZE(v) < 0 ? -1 : 1);
}
/* bits_in_digit(d) returns the unique integer k such that 2**(k-1) <= d <
2**k if d is nonzero, else 0. */
static const unsigned char BitLengthTable[32] = {
0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5
};
static int
bits_in_digit(digit d)
{
int d_bits = 0;
while (d >= 32) {
d_bits += 6;
d >>= 6;
}
d_bits += (int)BitLengthTable[d];
return d_bits;
}
size_t
_PyLong_NumBits(PyObject *vv)
{
PyLongObject *v = (PyLongObject *)vv;
size_t result = 0;
Py_ssize_t ndigits;
int msd_bits;
assert(v != NULL);
assert(PyLong_Check(v));
ndigits = Py_ABS(Py_SIZE(v));
assert(ndigits == 0 || v->ob_digit[ndigits - 1] != 0);
if (ndigits > 0) {
digit msd = v->ob_digit[ndigits - 1];
if ((size_t)(ndigits - 1) > SIZE_MAX / (size_t)PyLong_SHIFT)
goto Overflow;
result = (size_t)(ndigits - 1) * (size_t)PyLong_SHIFT;
msd_bits = bits_in_digit(msd);
if (SIZE_MAX - msd_bits < result)
goto Overflow;
result += msd_bits;
}
return result;
Overflow:
PyErr_SetString(PyExc_OverflowError, "int has too many bits "
"to express in a platform size_t");
return (size_t)-1;
}
PyObject *
_PyLong_FromByteArray(const unsigned char* bytes, size_t n,
int little_endian, int is_signed)
{
const unsigned char* pstartbyte; /* LSB of bytes */
int incr; /* direction to move pstartbyte */
const unsigned char* pendbyte; /* MSB of bytes */
size_t numsignificantbytes; /* number of bytes that matter */
Py_ssize_t ndigits; /* number of Python int digits */
PyLongObject* v; /* result */
Py_ssize_t idigit = 0; /* next free index in v->ob_digit */
if (n == 0)
return PyLong_FromLong(0L);
if (little_endian) {
pstartbyte = bytes;
pendbyte = bytes + n - 1;
incr = 1;
}
else {
pstartbyte = bytes + n - 1;
pendbyte = bytes;
incr = -1;
}
if (is_signed)
is_signed = *pendbyte >= 0x80;
/* Compute numsignificantbytes. This consists of finding the most
significant byte. Leading 0 bytes are insignificant if the number
is positive, and leading 0xff bytes if negative. */
{
size_t i;
const unsigned char* p = pendbyte;
const int pincr = -incr; /* search MSB to LSB */
const unsigned char insignificant = is_signed ? 0xff : 0x00;
for (i = 0; i < n; ++i, p += pincr) {
if (*p != insignificant)
break;
}
numsignificantbytes = n - i;
/* 2's-comp is a bit tricky here, e.g. 0xff00 == -0x0100, so
actually has 2 significant bytes. OTOH, 0xff0001 ==
-0x00ffff, so we wouldn't *need* to bump it there; but we
do for 0xffff = -0x0001. To be safe without bothering to
check every case, bump it regardless. */
if (is_signed && numsignificantbytes < n)
++numsignificantbytes;
}
/* How many Python int digits do we need? We have
8*numsignificantbytes bits, and each Python int digit has
PyLong_SHIFT bits, so it's the ceiling of the quotient. */
/* catch overflow before it happens */
if (numsignificantbytes > (PY_SSIZE_T_MAX - PyLong_SHIFT) / 8) {
PyErr_SetString(PyExc_OverflowError,
"byte array too long to convert to int");
return NULL;
}
ndigits = (numsignificantbytes * 8 + PyLong_SHIFT - 1) / PyLong_SHIFT;
v = _PyLong_New(ndigits);
if (v == NULL)
return NULL;
/* Copy the bits over. The tricky parts are computing 2's-comp on
the fly for signed numbers, and dealing with the mismatch between
8-bit bytes and (probably) 15-bit Python digits.*/
{
size_t i;
twodigits carry = 1; /* for 2's-comp calculation */
twodigits accum = 0; /* sliding register */
unsigned int accumbits = 0; /* number of bits in accum */
const unsigned char* p = pstartbyte;
for (i = 0; i < numsignificantbytes; ++i, p += incr) {
twodigits thisbyte = *p;
/* Compute correction for 2's comp, if needed. */
if (is_signed) {
thisbyte = (0xff ^ thisbyte) + carry;
carry = thisbyte >> 8;
thisbyte &= 0xff;
}
/* Because we're going LSB to MSB, thisbyte is
more significant than what's already in accum,
so needs to be prepended to accum. */
accum |= thisbyte << accumbits;
accumbits += 8;
if (accumbits >= PyLong_SHIFT) {
/* There's enough to fill a Python digit. */
assert(idigit < ndigits);
v->ob_digit[idigit] = (digit)(accum & PyLong_MASK);
++idigit;
accum >>= PyLong_SHIFT;
accumbits -= PyLong_SHIFT;
assert(accumbits < PyLong_SHIFT);
}
}
assert(accumbits < PyLong_SHIFT);
if (accumbits) {
assert(idigit < ndigits);
v->ob_digit[idigit] = (digit)accum;
++idigit;
}
}
Py_SIZE(v) = is_signed ? -idigit : idigit;
return (PyObject *)long_normalize(v);
}
int
_PyLong_AsByteArray(PyLongObject* v,
unsigned char* bytes, size_t n,
int little_endian, int is_signed)
{
Py_ssize_t i; /* index into v->ob_digit */
Py_ssize_t ndigits; /* |v->ob_size| */
twodigits accum; /* sliding register */
unsigned int accumbits; /* # bits in accum */
int do_twos_comp; /* store 2's-comp? is_signed and v < 0 */
digit carry; /* for computing 2's-comp */
size_t j; /* # bytes filled */
unsigned char* p; /* pointer to next byte in bytes */
int pincr; /* direction to move p */
assert(v != NULL && PyLong_Check(v));
if (Py_SIZE(v) < 0) {
ndigits = -(Py_SIZE(v));
if (!is_signed) {
PyErr_SetString(PyExc_OverflowError,
"can't convert negative int to unsigned");
return -1;
}
do_twos_comp = 1;
}
else {
ndigits = Py_SIZE(v);
do_twos_comp = 0;
}
if (little_endian) {
p = bytes;
pincr = 1;
}
else {
p = bytes + n - 1;
pincr = -1;
}
/* Copy over all the Python digits.
It's crucial that every Python digit except for the MSD contribute
exactly PyLong_SHIFT bits to the total, so first assert that the int is
normalized. */
assert(ndigits == 0 || v->ob_digit[ndigits - 1] != 0);
j = 0;
accum = 0;
accumbits = 0;
carry = do_twos_comp ? 1 : 0;
for (i = 0; i < ndigits; ++i) {
digit thisdigit = v->ob_digit[i];
if (do_twos_comp) {
thisdigit = (thisdigit ^ PyLong_MASK) + carry;
carry = thisdigit >> PyLong_SHIFT;
thisdigit &= PyLong_MASK;
}
/* Because we're going LSB to MSB, thisdigit is more
significant than what's already in accum, so needs to be
prepended to accum. */
accum |= (twodigits)thisdigit << accumbits;
/* The most-significant digit may be (probably is) at least
partly empty. */
if (i == ndigits - 1) {
/* Count # of sign bits -- they needn't be stored,
* although for signed conversion we need later to
* make sure at least one sign bit gets stored. */
digit s = do_twos_comp ? thisdigit ^ PyLong_MASK : thisdigit;
while (s != 0) {
s >>= 1;
accumbits++;
}
}
else
accumbits += PyLong_SHIFT;
/* Store as many bytes as possible. */
while (accumbits >= 8) {
if (j >= n)
goto Overflow;
++j;
*p = (unsigned char)(accum & 0xff);
p += pincr;
accumbits -= 8;
accum >>= 8;
}
}
/* Store the straggler (if any). */
assert(accumbits < 8);
assert(carry == 0); /* else do_twos_comp and *every* digit was 0 */
if (accumbits > 0) {
if (j >= n)
goto Overflow;
++j;
if (do_twos_comp) {
/* Fill leading bits of the byte with sign bits
(appropriately pretending that the int had an
infinite supply of sign bits). */
accum |= (~(twodigits)0) << accumbits;
}
*p = (unsigned char)(accum & 0xff);
p += pincr;
}
else if (j == n && n > 0 && is_signed) {
/* The main loop filled the byte array exactly, so the code
just above didn't get to ensure there's a sign bit, and the
loop below wouldn't add one either. Make sure a sign bit
exists. */
unsigned char msb = *(p - pincr);
int sign_bit_set = msb >= 0x80;
assert(accumbits == 0);
if (sign_bit_set == do_twos_comp)
return 0;
else
goto Overflow;
}