Objects/longobject.c (part 4)

Source:

cpython 3.14 @ ab2d84fe1023/Objects/longobject.c ↗

This annotation covers integer formatting, conversion to float, and bitwise operations. See objects_longobject3_detail for the core arithmetic.

Map

Lines	Symbol	Role
1-200	long_format	bin(), oct(), hex(), format(n, 'x')
201-400	PyLong_AsDouble, long_float	Conversion to float with overflow check
401-600	long_and, long_or, long_xor, long_invert	Bitwise operations
601-800	long_lshift, long_rshift	Shift operations
801-1000	long_to_bytes, long_from_bytes	int.to_bytes, int.from_bytes
1001-1200	long_gcd	math.gcd backend

Reading

bin/oct/hex formatting

// CPython: Objects/longobject.c:85 long_format
static PyObject *
long_format(PyObject *aa, int base)
{
    /* Convert to base 2/8/10/16 string */
    PyObject *v = PyLong_Format(aa, base);
    return v;
}

bin(255) calls long_format(n, 2). The format includes the 0b/0o/0x prefix.

Conversion to float

// CPython: Objects/longobject.c:280 PyLong_AsDouble
double
PyLong_AsDouble(PyObject *vv)
{
    /* Return INFINITY if the integer is too large for a double */
    if (Py_ABS(Py_SIZE(v)) > DBL_MAX_EXP / PyLong_SHIFT) {
        PyErr_SetString(PyExc_OverflowError,
                        "int too large to convert to float");
        return -1.0;
    }
    return _PyLong_IsZero(v) ? 0.0 : _PyLong_Frexp(v, &exponent) * pow(2.0, exponent);
}

Bitwise left shift

// CPython: Objects/longobject.c:620 long_lshift
static PyObject *
long_lshift(PyObject *a, PyObject *b)
{
    PyLongObject *shiftby = (PyLongObject *)b;
    Py_ssize_t wordshift = shiftby->ob_digit[0] / PyLong_SHIFT;
    int remshift = shiftby->ob_digit[0] % PyLong_SHIFT;
    /* Allocate result with extra digits */
    PyLongObject *z = _PyLong_New(Py_SIZE(a) + wordshift + 1);
    /* Copy digits shifted by wordshift positions */
    ...
    /* Apply remshift within each digit */
    ...
}

Left shift by n is a * 2^n. For large shifts this grows the digit array.

int.to_bytes

// CPython: Objects/longobject.c:900 long_to_bytes_impl
static PyObject *
long_to_bytes_impl(PyObject *self, Py_ssize_t length, const char *byteorder,
                   int signed_)
{
    /* Convert to big or little endian byte array of exactly 'length' bytes */
    ...
    Py_ssize_t nbytes = (bit_length + 7) / 8;
    if (nbytes > length) {
        PyErr_SetString(PyExc_OverflowError, "int too big to convert");
        return NULL;
    }
    ...
}

(255).to_bytes(2, 'big') gives b'\x00\xff'.

gopy notes

bin/oct/hex are in objects/int.go. PyLong_AsDouble maps to Go's big.Int.Float64() with overflow detection. Bitwise operations use Go's big.Int And, Or, Xor, Lsh, Rsh. int.to_bytes/from_bytes use big.Int.Bytes() and big.Int.SetBytes() with endian conversion.