numpy · ngoldbaum · Dec 24, 2023 · Nov 17, 2023 · Nov 20, 2023 · Dec 6, 2023
diff --git a/numpy/_core/code_generators/generate_umath.py b/numpy/_core/code_generators/generate_umath.py
@@ -1187,6 +1187,11 @@ def english_upper(s):
           docstrings.get('numpy._core.umath.count'),
           None,
           ),
+'_replace':
+    Ufunc(4, 1, None,
+          docstrings.get('numpy.core.umath._replace'),
+          None,
+          ),
 'startswith':
     Ufunc(4, 1, False_,
           docstrings.get('numpy._core.umath.startswith'),

diff --git a/numpy/_core/code_generators/ufunc_docstrings.py b/numpy/_core/code_generators/ufunc_docstrings.py
@@ -4558,6 +4558,13 @@ def add_newdoc(place, name, doc):
 
     """)
 
+add_newdoc('numpy.core.umath', '_replace',
+    """
+    UFunc implementation of ``replace``. This internal function
+    is called by ``replace`` with ``out`` set, so that the
+    size of the resulting string buffer is known.
+    """)
+
 add_newdoc('numpy._core.umath', 'startswith',
     """
     Returns a boolean array which is `True` where the string element

diff --git a/numpy/_core/defchararray.py b/numpy/_core/defchararray.py
@@ -1261,8 +1261,19 @@ def replace(a, old, new, count=None):
     >>> np.char.replace(a, 'is', 'was')
     array(['The dwash was fresh', 'Thwas was it'], dtype='<U19')
     """
-    return _to_bytes_or_str_array(
-        _vec_string(a, object_, 'replace', [old, new] + _clean_args(count)), a)
+    max_int64 = numpy.iinfo(numpy.int64).max
+    count = count if count is not None else max_int64
+
+    counts = numpy._core.umath.count(a, old, 0, max_int64)
+    buffersizes = (
+        numpy._core.umath.str_len(a)
+        + counts * (numpy._core.umath.str_len(new) -
+                    numpy._core.umath.str_len(old))
+    )
+    max_buffersize = numpy.max(buffersizes)
+    out = numpy.empty(a.shape, dtype=f"{a.dtype.char}{max_buffersize}")
+    numpy._core.umath._replace(a, old, new, count, out=out)
+    return out
 
 
 @array_function_dispatch(_count_dispatcher)
@@ -2506,7 +2517,7 @@ def replace(self, old, new, count=None):
         char.replace
 
         """
-        return asarray(replace(self, old, new, count))
+        return replace(self, old, new, count)
 
     def rfind(self, sub, start=0, end=None):
         """

diff --git a/numpy/_core/src/umath/string_buffer.h b/numpy/_core/src/umath/string_buffer.h
@@ -256,6 +256,63 @@ struct Buffer {
         }
         return true;
     }
+
+    inline Buffer<enc>
+    rstrip()
+    {
+        Buffer<enc> tmp(after, 0);
+        tmp--;
+        while (tmp >= *this && (*tmp == '\0' || NumPyOS_ascii_isspace(*tmp))) {
+            tmp--;
+        }
+        tmp++;
+
+        after = tmp.buf;
+        return *this;
+    }
+
+    inline int
+    strcmp(Buffer<enc> other, bool rstrip)
+    {
+        Buffer tmp1 = rstrip ? this->rstrip() : *this;
+        Buffer tmp2 = rstrip ? other.rstrip() : other;
+
+        while (tmp1.buf < tmp1.after && tmp2.buf < tmp2.after) {
+            if (*tmp1 < *tmp2) {
+                return -1;
+            }
+            if (*tmp1 > *tmp2) {
+                return 1;
+            }
+            tmp1++;
+            tmp2++;
+        }
+        while (tmp1.buf < tmp1.after) {
+            if (*tmp1 < 0) {
+                return -1;
+            }
+            if (*tmp1 > 0) {
+                return 1;
+            }
+            tmp1++;
+        }
+        while (tmp2.buf < tmp2.after) {
+            if (*tmp2 < 0) {
+                return -1;
+            }
+            if (*tmp2 > 0) {
+                return 1;
+            }
+            tmp2++;
+        }
+        return 0;
+    }
+
+    inline int
+    strcmp(Buffer<enc> other)
+    {
+        return strcmp(other, false);
+    }
 };