Optimise internal bounds checks like "0 <= i <= limit" using a single unsigned comparison.

See https://bugs.python.org/issue28397

Cython/Utility/MemoryView_C.c

@@ -857,7 +857,7 @@ if (unlikely(__pyx_memoryview_slice_memviewslice(
     if ({{wraparound}} && (__pyx_tmp_idx < 0))
         __pyx_tmp_idx += __pyx_tmp_shape;
 
-    if ({{boundscheck}} && (__pyx_tmp_idx < 0 || __pyx_tmp_idx >= __pyx_tmp_shape)) {
+    if ({{boundscheck}} && !__Pyx_is_valid_index(__pyx_tmp_idx, __pyx_tmp_shape)) {
         {{if not have_gil}}
             #ifdef WITH_THREAD
             PyGILState_STATE __pyx_gilstate_save = PyGILState_Ensure();

Cython/Utility/ObjectHandling.c

@@ -398,7 +398,7 @@ static CYTHON_INLINE PyObject *__Pyx_GetItemInt_{{type}}_Fast(PyObject *o, Py_ss
     if (wraparound & unlikely(i < 0)) {
         wrapped_i += Py{{type}}_GET_SIZE(o);
     }
-    if ((!boundscheck) || likely((0 <= wrapped_i) & (wrapped_i < Py{{type}}_GET_SIZE(o)))) {
+    if ((!boundscheck) || likely(__Pyx_is_valid_index(wrapped_i, Py{{type}}_GET_SIZE(o)))) {
         PyObject *r = Py{{type}}_GET_ITEM(o, wrapped_i);
         Py_INCREF(r);
         return r;
@@ -416,7 +416,7 @@ static CYTHON_INLINE PyObject *__Pyx_GetItemInt_Fast(PyObject *o, Py_ssize_t i,
 #if CYTHON_ASSUME_SAFE_MACROS && !CYTHON_AVOID_BORROWED_REFS && CYTHON_USE_TYPE_SLOTS
     if (is_list || PyList_CheckExact(o)) {
         Py_ssize_t n = ((!wraparound) | likely(i >= 0)) ? i : i + PyList_GET_SIZE(o);
-        if ((!boundscheck) || (likely((n >= 0) & (n < PyList_GET_SIZE(o))))) {
+        if ((!boundscheck) || (likely(__Pyx_is_valid_index(n, PyList_GET_SIZE(o))))) {
             PyObject *r = PyList_GET_ITEM(o, n);
             Py_INCREF(r);
             return r;
@@ -424,7 +424,7 @@ static CYTHON_INLINE PyObject *__Pyx_GetItemInt_Fast(PyObject *o, Py_ssize_t i,
     }
     else if (PyTuple_CheckExact(o)) {
         Py_ssize_t n = ((!wraparound) | likely(i >= 0)) ? i : i + PyTuple_GET_SIZE(o);
-        if ((!boundscheck) || likely((n >= 0) & (n < PyTuple_GET_SIZE(o)))) {
+        if ((!boundscheck) || likely(__Pyx_is_valid_index(n, PyTuple_GET_SIZE(o)))) {
             PyObject *r = PyTuple_GET_ITEM(o, n);
             Py_INCREF(r);
             return r;
@@ -482,7 +482,7 @@ static CYTHON_INLINE int __Pyx_SetItemInt_Fast(PyObject *o, Py_ssize_t i, PyObje
 #if CYTHON_ASSUME_SAFE_MACROS && !CYTHON_AVOID_BORROWED_REFS && CYTHON_USE_TYPE_SLOTS
     if (is_list || PyList_CheckExact(o)) {
         Py_ssize_t n = (!wraparound) ? i : ((likely(i >= 0)) ? i : i + PyList_GET_SIZE(o));
-        if ((!boundscheck) || likely((n >= 0) & (n < PyList_GET_SIZE(o)))) {
+        if ((!boundscheck) || likely(__Pyx_is_valid_index(n, PyList_GET_SIZE(o)))) {
             PyObject* old = PyList_GET_ITEM(o, n);
             Py_INCREF(v);
             PyList_SET_ITEM(o, n, v);

Cython/Utility/Optimize.c

@@ -165,7 +165,7 @@ static PyObject* __Pyx__PyList_PopIndex(PyObject* L, PyObject* py_ix, Py_ssize_t
         if (cix < 0) {
             cix += size;
         }
-        if (likely(0 <= cix && cix < size)) {
+        if (likely(__Pyx_is_valid_index(cix, size))) {
             PyObject* v = PyList_GET_ITEM(L, cix);
             Py_SIZE(L) -= 1;
             size -= 1;

Cython/Utility/StringTools.c

@@ -331,7 +331,7 @@ static CYTHON_INLINE int __Pyx_GetItemInt_ByteArray_Fast(PyObject* string, Py_ss
     if (wraparound | boundscheck) {
         length = PyByteArray_GET_SIZE(string);
         if (wraparound & unlikely(i < 0)) i += length;
-        if ((!boundscheck) || likely((0 <= i) & (i < length))) {
+        if ((!boundscheck) || likely(__Pyx_is_valid_index(i, length))) {
             return (unsigned char) (PyByteArray_AS_STRING(string)[i]);
         } else {
             PyErr_SetString(PyExc_IndexError, "bytearray index out of range");
@@ -361,7 +361,7 @@ static CYTHON_INLINE int __Pyx_SetItemInt_ByteArray_Fast(PyObject* string, Py_ss
     if (wraparound | boundscheck) {
         length = PyByteArray_GET_SIZE(string);
         if (wraparound & unlikely(i < 0)) i += length;
-        if ((!boundscheck) || likely((0 <= i) & (i < length))) {
+        if ((!boundscheck) || likely(__Pyx_is_valid_index(i, length))) {
             PyByteArray_AS_STRING(string)[i] = (char) v;
             return 0;
         } else {
@@ -394,7 +394,7 @@ static CYTHON_INLINE Py_UCS4 __Pyx_GetItemInt_Unicode_Fast(PyObject* ustring, Py
     if (wraparound | boundscheck) {
         length = __Pyx_PyUnicode_GET_LENGTH(ustring);
         if (wraparound & unlikely(i < 0)) i += length;
-        if ((!boundscheck) || likely((0 <= i) & (i < length))) {
+        if ((!boundscheck) || likely(__Pyx_is_valid_index(i, length))) {
             return __Pyx_PyUnicode_READ_CHAR(ustring, i);
         } else {
             PyErr_SetString(PyExc_IndexError, "string index out of range");
@@ -752,15 +752,15 @@ static CYTHON_INLINE char __Pyx_PyBytes_GetItemInt(PyObject* bytes, Py_ssize_t i
 /////////////// bytes_index ///////////////
 
 static CYTHON_INLINE char __Pyx_PyBytes_GetItemInt(PyObject* bytes, Py_ssize_t index, int check_bounds) {
+    if (index < 0)
+        index += PyBytes_GET_SIZE(bytes);
     if (check_bounds) {
         Py_ssize_t size = PyBytes_GET_SIZE(bytes);
-        if (unlikely(index >= size) | ((index < 0) & unlikely(index < -size))) {
+        if (unlikely(!__Pyx_is_valid_index(index, size))) {
             PyErr_SetString(PyExc_IndexError, "string index out of range");
             return (char) -1;
         }
     }
-    if (index < 0)
-        index += PyBytes_GET_SIZE(bytes);
     return PyBytes_AS_STRING(bytes)[index];
 }
 
@@ -990,7 +990,7 @@ static CYTHON_INLINE int __Pyx_PyByteArray_AppendObject(PyObject* bytearray, PyO
     {
         // CPython calls PyNumber_Index() internally
         ival = __Pyx_PyIndex_AsSsize_t(value);
-        if (unlikely((ival < 0) | (ival > 255))) {
+        if (unlikely(!__Pyx_is_valid_index(ival, 256))) {
             if (ival == -1 && PyErr_Occurred())
                 return -1;
             goto bad_range;
@@ -1012,7 +1012,7 @@ static CYTHON_INLINE int __Pyx_PyByteArray_Append(PyObject* bytearray, int value
 static CYTHON_INLINE int __Pyx_PyByteArray_Append(PyObject* bytearray, int value) {
     PyObject *pyval, *retval;
 #if CYTHON_COMPILING_IN_CPYTHON
-    if (likely((value >= 0) & (value <= 255))) {
+    if (likely(__Pyx_is_valid_index(value, 256))) {
         Py_ssize_t n = Py_SIZE(bytearray);
         if (likely(n != PY_SSIZE_T_MAX)) {
             if (unlikely(PyByteArray_Resize(bytearray, n + 1) < 0))

Cython/Utility/TypeConversion.c

@@ -16,6 +16,14 @@
           (is_signed || likely(v < (type)PY_SSIZE_T_MAX ||        \
                                v == (type)PY_SSIZE_T_MAX)))  )
 
+static CYTHON_INLINE int __Pyx_is_valid_index(Py_ssize_t i, Py_ssize_t limit) {
+    // Optimisation from Section 14.2 "Bounds Checking" in
+    //   https://www.agner.org/optimize/optimizing_cpp.pdf
+    // See https://bugs.python.org/issue28397
+    // The cast to unsigned effectively tests for "0 <= i < limit".
+    return (size_t) i < (size_t) limit;
+}
+
 // fast and unsafe abs(Py_ssize_t) that ignores the overflow for (-PY_SSIZE_T_MAX-1)
 #if defined (__cplusplus) && __cplusplus >= 201103L
     #include <cstdlib>
@@ -529,18 +537,23 @@ static Py_UCS4 __Pyx__PyObject_AsPy_UCS4(PyObject*);
 
 /////////////// ObjectAsUCS4 ///////////////
 
-static Py_UCS4 __Pyx__PyObject_AsPy_UCS4(PyObject* x) {
-   long ival;
-   ival = __Pyx_PyInt_As_long(x);
-   if (unlikely(ival < 0)) {
+static Py_UCS4 __Pyx__PyObject_AsPy_UCS4_raise_error(long ival) {
+   if (ival < 0) {
        if (!PyErr_Occurred())
            PyErr_SetString(PyExc_OverflowError,
                            "cannot convert negative value to Py_UCS4");
-       return (Py_UCS4)-1;
-   } else if (unlikely(ival > 1114111)) {
+   } else {
        PyErr_SetString(PyExc_OverflowError,
                        "value too large to convert to Py_UCS4");
+   }
    return (Py_UCS4)-1;
+}
+
+static Py_UCS4 __Pyx__PyObject_AsPy_UCS4(PyObject* x) {
+   long ival;
+   ival = __Pyx_PyInt_As_long(x);
+   if (unlikely(!__Pyx_is_valid_index(ival, 1114111 + 1))) {
+       return __Pyx__PyObject_AsPy_UCS4_raise_error(ival);
    }
    return (Py_UCS4)ival;
 }
@@ -582,14 +595,16 @@ static CYTHON_INLINE Py_UNICODE __Pyx_PyObject_AsPy_UNICODE(PyObject* x) {
         #endif
         ival = __Pyx_PyInt_As_long(x);
     }
-    if (unlikely(ival < 0)) {
+    if (unlikely(!__Pyx_is_valid_index(ival, maxval + 1))) {
+        if (ival < 0) {
             if (!PyErr_Occurred())
                 PyErr_SetString(PyExc_OverflowError,
                                 "cannot convert negative value to Py_UNICODE");
             return (Py_UNICODE)-1;
-    } else if (unlikely(ival > maxval)) {
+        } else {
             PyErr_SetString(PyExc_OverflowError,
                             "value too large to convert to Py_UNICODE");
+        }
         return (Py_UNICODE)-1;
     }
     return (Py_UNICODE)ival;