bpo-43422: Revert _decimal C API addition (GH-24960)

Stefan Krah requested the reversal of these (unreleased) changes, quoting him:
> The capsule API does not meet my testing standards, since I've focused
on the upstream mpdecimal in the last couple of months.
> Additionally, I'd like to refine the API, perhaps together with the
Arrow community.

Automerge-Triggered-By: GH:pitrou

2 files changed, 0 insertions, 232 deletions

diff --git a/Doc/c-api/concrete.rst b/Doc/c-api/concrete.rst
index bf263d6..c1d9fa1 100644
--- a/Doc/c-api/concrete.rst
+++ b/Doc/c-api/concrete.rst
@@ -115,4 +115,3 @@ Other Objects
    coro.rst
    contextvars.rst
    datetime.rst
-   decimal.rst
diff --git a/Doc/c-api/decimal.rst b/Doc/c-api/decimal.rst
deleted file mode 100644
index 94cc4a7..0000000
--- a/Doc/c-api/decimal.rst
+++ /dev/null
@@ -1,231 +0,0 @@
-.. sectionauthor:: Stefan Krah
-
-.. highlight:: c
-
-
-Decimal capsule API
-===================
-
-Capsule API functions can be used in the same manner as regular library
-functions, provided that the API has been initialized.
-
-
-Initialize
-----------
-
-Typically, a C extension module that uses the decimal API will do these
-steps in its init function:
-
-.. code-block:: c
-
-    #include "pydecimal.h"
-
-    static int decimal_initialized = 0;
-    if (!decimal_initialized) {
-        if (import_decimal() < 0) {
-            return NULL;
-        }
-
-        decimal_initialized = 1;
-    }
-
-
-Type checking, predicates, accessors
-------------------------------------
-
-.. c:function:: int PyDec_TypeCheck(const PyObject *dec)
-
-   Return 1 if ``dec`` is a Decimal, 0 otherwise.  This function does not set
-   any exceptions.
-
-
-.. c:function:: int PyDec_IsSpecial(const PyObject *dec)
-
-   Return 1 if ``dec`` is ``NaN``, ``sNaN`` or ``Infinity``, 0 otherwise.
-
-   Set TypeError and return -1 if ``dec`` is not a Decimal.  It is guaranteed that
-   this is the only failure mode, so if ``dec`` has already been type-checked, no
-   errors can occur and the function can be treated as a simple predicate.
-
-
-.. c:function:: int PyDec_IsNaN(const PyObject *dec)
-
-   Return 1 if ``dec`` is ``NaN`` or ``sNaN``, 0 otherwise.
-
-   Set TypeError and return -1 if ``dec`` is not a Decimal.  It is guaranteed that
-   this is the only failure mode, so if ``dec`` has already been type-checked, no
-   errors can occur and the function can be treated as a simple predicate.
-
-
-.. c:function:: int PyDec_IsInfinite(const PyObject *dec)
-
-   Return 1 if ``dec`` is ``Infinity``, 0 otherwise.
-
-   Set TypeError and return -1 if ``dec`` is not a Decimal.  It is guaranteed that
-   this is the only failure mode, so if ``dec`` has already been type-checked, no
-   errors can occur and the function can be treated as a simple predicate.
-
-
-.. c:function:: int64_t PyDec_GetDigits(const PyObject *dec)
-
-   Return the number of digits in the coefficient.  For ``Infinity``, the
-   number of digits is always zero.  Typically, the same applies to ``NaN``
-   and ``sNaN``, but both of these can have a payload that is equivalent to
-   a coefficient.  Therefore, ``NaNs`` can have a nonzero return value.
-
-   Set TypeError and return -1 if ``dec`` is not a Decimal.  It is guaranteed that
-   this is the only failure mode, so if ``dec`` has already been type-checked, no
-   errors can occur and the function can be treated as a simple accessor.
-
-
-Exact conversions between decimals and primitive C types
---------------------------------------------------------
-
-This API supports conversions for decimals with a coefficient up to 38 digits.
-
-Data structures
-~~~~~~~~~~~~~~~
-
-The conversion functions use the following status codes and data structures:
-
-.. code-block:: c
-
-   /* status cases for getting a triple */
-   enum mpd_triple_class {
-     MPD_TRIPLE_NORMAL,
-     MPD_TRIPLE_INF,
-     MPD_TRIPLE_QNAN,
-     MPD_TRIPLE_SNAN,
-     MPD_TRIPLE_ERROR,
-   };
-
-   typedef struct {
-     enum mpd_triple_class tag;
-     uint8_t sign;
-     uint64_t hi;
-     uint64_t lo;
-     int64_t exp;
-   } mpd_uint128_triple_t;
-
-The status cases are explained below.  ``sign`` is 0 for positive and 1 for negative.
-``((uint128_t)hi << 64) + lo`` is the coefficient, ``exp`` is the exponent.
-
-The data structure is called "triple" because the decimal triple (sign, coeff, exp)
-is an established term and (``hi``, ``lo``) represents a single ``uint128_t`` coefficient.
-
-
-Functions
-~~~~~~~~~
-
-.. c:function:: mpd_uint128_triple_t PyDec_AsUint128Triple(const PyObject *dec)
-
-   Convert a decimal to a triple.  As above, it is guaranteed that the only
-   Python failure mode is a TypeError, checks can be omitted if the type is
-   known.
-
-   For simplicity, the usage of the function and all special cases are
-   explained in code form and comments:
-
-.. code-block:: c
-
-    triple = PyDec_AsUint128Triple(dec);
-    switch (triple.tag) {
-    case MPD_TRIPLE_QNAN:
-        /*
-         * Success: handle a quiet NaN.
-         *   1) triple.sign is 0 or 1.
-         *   2) triple.exp is always 0.
-         *   3) If triple.hi or triple.lo are nonzero, the NaN has a payload.
-         */
-        break;
-
-    case MPD_TRIPLE_SNAN:
-        /*
-         * Success: handle a signaling NaN.
-         *   1) triple.sign is 0 or 1.
-         *   2) triple.exp is always 0.
-         *   3) If triple.hi or triple.lo are nonzero, the sNaN has a payload.
-         */
-        break;
-
-    case MPD_TRIPLE_INF:
-        /*
-         * Success: handle Infinity.
-         *   1) triple.sign is 0 or 1.
-         *   2) triple.exp is always 0.
-         *   3) triple.hi and triple.lo are always zero.
-         */
-        break;
-
-    case MPD_TRIPLE_NORMAL:
-        /* Success: handle a finite value. */
-        break;
-
-    case MPD_TRIPLE_ERROR:
-        /* TypeError check: can be omitted if the type of dec is known. */
-        if (PyErr_Occurred()) {
-            return NULL;
-        }
-
-        /* Too large for conversion.  PyDec_AsUint128Triple() does not set an
-           exception so applications can choose themselves.  Typically this
-           would be a ValueError. */
-        PyErr_SetString(PyExc_ValueError,
-            "value out of bounds for a uint128 triple");
-        return NULL;
-    }
-
-.. c:function:: PyObject *PyDec_FromUint128Triple(const mpd_uint128_triple_t *triple)
-
-   Create a decimal from a triple.  The following rules must be observed for
-   initializing the triple:
-
-   1) ``triple.sign`` must always be 0 (for positive) or 1 (for negative).
-
-   2) ``MPD_TRIPLE_QNAN``: ``triple.exp`` must be 0.  If ``triple.hi`` or ``triple.lo``
-      are nonzero,  create a ``NaN`` with a payload.
-
-   3) ``MPD_TRIPLE_SNAN``: ``triple.exp`` must be 0. If ``triple.hi`` or ``triple.lo``
-      are nonzero,  create an ``sNaN`` with a payload.
-
-   4) ``MPD_TRIPLE_INF``: ``triple.exp``, ``triple.hi`` and ``triple.lo`` must be zero.
-
-   5) ``MPD_TRIPLE_NORMAL``: ``MPD_MIN_ETINY + 38 < triple.exp < MPD_MAX_EMAX - 38``.
-      ``triple.hi`` and ``triple.lo`` can be chosen freely.
-
-   6) ``MPD_TRIPLE_ERROR``: It is always an error to set this tag.
-
-
-   If one of the above conditions is not met, the function returns ``NaN`` if
-   the ``InvalidOperation`` trap is not set in the thread local context.  Otherwise,
-   it sets the ``InvalidOperation`` exception and returns NULL.
-
-   Additionally, though extremely unlikely give the small allocation sizes,
-   the function can set ``MemoryError`` and return ``NULL``.
-
-
-Advanced API
-------------
-
-This API enables the use of ``libmpdec`` functions.  Since Python is compiled with
-hidden symbols, the API requires an external libmpdec and the ``mpdecimal.h``
-header.
-
-
-Functions
-~~~~~~~~~
-
-.. c:function:: PyObject *PyDec_Alloc(void)
-
-   Return a new decimal that can be used in the ``result`` position of ``libmpdec``
-   functions.
-
-.. c:function:: mpd_t *PyDec_Get(PyObject *v)
-
-   Get a pointer to the internal ``mpd_t`` of the decimal.  Decimals are immutable,
-   so this function must only be used on a new Decimal that has been created by
-   PyDec_Alloc().
-
-.. c:function:: const mpd_t *PyDec_GetConst(const PyObject *v)
-
-   Get a pointer to the constant internal ``mpd_t`` of the decimal.