python · vstinner · Jan 24, 2025 · Jul 6, 2024 · Dec 14, 2024 · Dec 14, 2024
diff --git a/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst b/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
@@ -0,0 +1,3 @@
+Convert the :mod:`decimal` module to use :pep:`757` API.  That offer some
+speedup, if integer part of the :class:`~decimal.Decimal` instance is small.
+Patch by Sergey B Kirpichev.
diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
@@ -3639,12 +3639,13 @@ dec_format(PyObject *dec, PyObject *args)
 static PyObject *
 dec_as_long(PyObject *dec, PyObject *context, int round)
 {
-    PyLongObject *pylong;
+    PyObject *pylong;
    digit *ob_digit;
    size_t n;
    mpd_t *x;
    mpd_context_t workctx;
    uint32_t status = 0;
+    const PyLongLayout *layout = PyLong_GetNativeLayout();

    if (mpd_isspecial(MPD(dec))) {
        if (mpd_isnan(MPD(dec))) {
@@ -3672,34 +3673,45 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
    }

    status = 0;
-    ob_digit = NULL;
+
+    int64_t val = mpd_qget_i64(x, &status);
+    if (!status) {
+        mpd_del(x);
+        return PyLong_FromInt64(val);
+    }
+
+    const uint8_t bpd = layout->bits_per_digit;
+    n = (mpd_sizeinbase(x, 2) + bpd - 1) / bpd;
+    PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), n,
+                                               (void**)&ob_digit);
+    /* mpd_sizeinbase can overestimate size by 1 digit, set it to zero. */
+    ob_digit[n-1] = 0;
+    if (writer == NULL) {
+        PyLongWriter_Discard(writer);
+        mpd_del(x);
+        return NULL;
+    }
+
+    status = 0;
 #if PYLONG_BITS_IN_DIGIT == 30
-    n = mpd_qexport_u32(&ob_digit, 0, PyLong_BASE, x, &status);
+    n = mpd_qexport_u32(&ob_digit, n, PyLong_BASE, x, &status);
 #elif PYLONG_BITS_IN_DIGIT == 15
-    n = mpd_qexport_u16(&ob_digit, 0, PyLong_BASE, x, &status);
+    n = mpd_qexport_u16(&ob_digit, n, PyLong_BASE, x, &status);
 #else
    #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"
 #endif

    if (n == SIZE_MAX) {
        PyErr_NoMemory();
+        PyLongWriter_Discard(writer);
        mpd_del(x);
        return NULL;
    }

-    if (n == 1) {
-        sdigit val = mpd_arith_sign(x) * ob_digit[0];
-        mpd_free(ob_digit);
-        mpd_del(x);
-        return PyLong_FromLong(val);
-    }
-
    assert(n > 0);
-    assert(!mpd_iszero(x));
-    pylong = _PyLong_FromDigits(mpd_isnegative(x), n, ob_digit);
-    mpd_free(ob_digit);
+    pylong = PyLongWriter_Finish(writer);
    mpd_del(x);
-    return (PyObject *) pylong;
+    return pylong;
 }

 /* Convert a Decimal to its exact integer ratio representation. */
-Original file line number
+Diff line change
@@ -0,0 +1,3 @@
+    Convert the :mod:`decimal` module to use :pep:`757` API.  That offer some
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+    speedup, if integer part of the :class:`~decimal.Decimal` instance is small.
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+    Patch by Sergey B Kirpichev.