From 444af6577d913b60f22f1b3d335927e5a98e0a32 Mon Sep 17 00:00:00 2001
From: Jukka Lehtosalo <jukka.lehtosalo@iki.fi>
Date: Tue, 25 Nov 2025 16:41:12 +0000
Subject: [PATCH 1/9] WIP optimize append and write

---
 mypyc/lib-rt/librt_strings.c          | 15 +------
 mypyc/lib-rt/librt_strings.h          | 61 ++++++++++++++++++++++++++-
 mypyc/lib-rt/mypyc_util.h             |  4 ++
 mypyc/primitives/librt_strings_ops.py |  4 +-
 4 files changed, 67 insertions(+), 17 deletions(-)

diff --git a/mypyc/lib-rt/librt_strings.c b/mypyc/lib-rt/librt_strings.c
index dcad4137e7f11..d403934b89154 100644
--- a/mypyc/lib-rt/librt_strings.c
+++ b/mypyc/lib-rt/librt_strings.c
@@ -7,24 +7,11 @@
 #include "librt_strings.h"
 
 #define CPY_BOOL_ERROR 2
-#define CPY_NONE_ERROR 2
-#define CPY_NONE 1
 
 //
 // BytesWriter
 //
 
-// Length of the default buffer embedded directly in a BytesWriter object
-#define WRITER_EMBEDDED_BUF_LEN 512
-
-typedef struct {
-    PyObject_HEAD
-    char *buf;  // Beginning of the buffer
-    Py_ssize_t len;  // Current length (number of bytes written)
-    Py_ssize_t capacity;  // Total capacity of the buffer
-    char data[WRITER_EMBEDDED_BUF_LEN];  // Default buffer
-} BytesWriterObject;
-
 #define _WRITE(data, type, v) \
     do { \
        *(type *)(((BytesWriterObject *)data)->buf + ((BytesWriterObject *)data)->len) = v; \
@@ -426,7 +413,7 @@ librt_strings_module_exec(PyObject *m)
         (void *)BytesWriter_internal,
         (void *)BytesWriter_getvalue_internal,
         (void *)BytesWriter_append_internal,
-        (void *)BytesWriter_write_internal,
+        (void *)_grow_buffer,
         (void *)BytesWriter_type_internal,
         (void *)BytesWriter_len_internal,
         (void *)BytesWriter_truncate_internal,
diff --git a/mypyc/lib-rt/librt_strings.h b/mypyc/lib-rt/librt_strings.h
index 75eae8451e553..ef5a43c654b7a 100644
--- a/mypyc/lib-rt/librt_strings.h
+++ b/mypyc/lib-rt/librt_strings.h
@@ -28,12 +28,23 @@ import_librt_strings(void)
 
 static void *LibRTStrings_API[LIBRT_STRINGS_API_LEN];
 
+// Length of the default buffer embedded directly in a BytesWriter object
+#define WRITER_EMBEDDED_BUF_LEN 512
+
+typedef struct {
+    PyObject_HEAD
+    char *buf;  // Beginning of the buffer
+    Py_ssize_t len;  // Current length (number of bytes written)
+    Py_ssize_t capacity;  // Total capacity of the buffer
+    char data[WRITER_EMBEDDED_BUF_LEN];  // Default buffer
+} BytesWriterObject;
+
 #define LibRTStrings_ABIVersion (*(int (*)(void)) LibRTStrings_API[0])
 #define LibRTStrings_APIVersion (*(int (*)(void)) LibRTStrings_API[1])
 #define LibRTStrings_BytesWriter_internal (*(PyObject* (*)(void)) LibRTStrings_API[2])
 #define LibRTStrings_BytesWriter_getvalue_internal (*(PyObject* (*)(PyObject *source)) LibRTStrings_API[3])
 #define LibRTStrings_BytesWriter_append_internal (*(char (*)(PyObject *source, uint8_t value)) LibRTStrings_API[4])
-#define LibRTStrings_BytesWriter_write_internal (*(char (*)(PyObject *source, PyObject *value)) LibRTStrings_API[5])
+#define LibRTStrings_ByteWriter_grow_buffer_internal (*(bool (*)(BytesWriterObject *obj, Py_ssize_t size)) LibRTStrings_API[5])
 #define LibRTStrings_BytesWriter_type_internal (*(PyTypeObject* (*)(void)) LibRTStrings_API[6])
 #define LibRTStrings_BytesWriter_len_internal (*(CPyTagged (*)(PyObject *self)) LibRTStrings_API[7])
 #define LibRTStrings_BytesWriter_truncate_internal (*(char (*)(PyObject *self, int64_t size)) LibRTStrings_API[8])
@@ -75,6 +86,54 @@ static inline bool CPyBytesWriter_Check(PyObject *obj) {
     return Py_TYPE(obj) == LibRTStrings_BytesWriter_type_internal();
 }
 
+static inline bool
+CPyBytesWriter_EnsureSize(BytesWriterObject *data, Py_ssize_t n) {
+    if (likely(data->capacity - data->len >= n)) {
+        return true;
+    } else {
+        return LibRTStrings_ByteWriter_grow_buffer_internal(data, n);
+    }
+}
+
+static inline char
+CPyBytesWriter_Append(PyObject *obj, uint8_t value) {
+    BytesWriterObject *self = (BytesWriterObject *)obj;
+    // Store length in a local variable to enable additional optimizations
+    Py_ssize_t len = self->len;
+    if (!CPyBytesWriter_EnsureSize(self, 1))
+        return CPY_NONE_ERROR;
+    self->buf[len] = value;
+    self->len = len + 1;
+    return CPY_NONE;
+}
+
+static char
+CPyBytesWriter_Write(PyObject *obj, PyObject *value) {
+    BytesWriterObject *self = (BytesWriterObject *)obj;
+    const char *data;
+    Py_ssize_t size;
+    if (likely(PyBytes_Check(value))) {
+        data = PyBytes_AS_STRING(value);
+        size = PyBytes_GET_SIZE(value);
+    } else {
+        data = PyByteArray_AS_STRING(value);
+        size = PyByteArray_GET_SIZE(value);
+    }
+    // Write bytes content.
+    if (!CPyBytesWriter_EnsureSize(self, size))
+        return CPY_NONE_ERROR;
+    if (size < 8) {
+        char *p = self->buf + self->len;
+        for (Py_ssize_t i = 0; i < size; i++) {
+            p[i] = data[i];
+        }
+    } else {
+        memcpy(self->buf + self->len, data, size);
+    }
+    self->len += size;
+    return CPY_NONE;
+}
+
 #endif  // MYPYC_EXPERIMENTAL
 
 #endif  // LIBRT_STRINGS_H
diff --git a/mypyc/lib-rt/mypyc_util.h b/mypyc/lib-rt/mypyc_util.h
index 50a806c91a8a6..6715d67d96572 100644
--- a/mypyc/lib-rt/mypyc_util.h
+++ b/mypyc/lib-rt/mypyc_util.h
@@ -142,6 +142,10 @@ typedef PyObject CPyModule;
 // Error value for floats
 #define CPY_FLOAT_ERROR -113.0
 
+// Value for 'None' primitive type
+#define CPY_NONE_ERROR 2
+#define CPY_NONE 1
+
 typedef void (*CPyVTableItem)(void);
 
 static inline CPyTagged CPyTagged_ShortFromInt(int x) {
diff --git a/mypyc/primitives/librt_strings_ops.py b/mypyc/primitives/librt_strings_ops.py
index 786784d15f60d..3545593f59cfe 100644
--- a/mypyc/primitives/librt_strings_ops.py
+++ b/mypyc/primitives/librt_strings_ops.py
@@ -38,7 +38,7 @@
     name="write",
     arg_types=[bytes_writer_rprimitive, bytes_rprimitive],
     return_type=none_rprimitive,
-    c_function_name="LibRTStrings_BytesWriter_write_internal",
+    c_function_name="CPyBytesWriter_Write",
     error_kind=ERR_MAGIC,
     experimental=True,
     dependencies=[LIBRT_STRINGS],
@@ -48,7 +48,7 @@
     name="append",
     arg_types=[bytes_writer_rprimitive, uint8_rprimitive],
     return_type=none_rprimitive,
-    c_function_name="LibRTStrings_BytesWriter_append_internal",
+    c_function_name="CPyBytesWriter_Append",
     error_kind=ERR_MAGIC,
     experimental=True,
     dependencies=[LIBRT_STRINGS],

From e6a6207d1985ff63fbdd17f33888c1f7af11606f Mon Sep 17 00:00:00 2001
From: Jukka Lehtosalo <jukka.lehtosalo@iki.fi>
Date: Tue, 25 Nov 2025 17:07:16 +0000
Subject: [PATCH 2/9] Add inline primitive for len

---
 mypyc/lib-rt/librt_strings.c               |  1 -
 mypyc/lib-rt/librt_strings.h               | 11 ++++++++---
 mypyc/primitives/librt_strings_ops.py      |  2 +-
 mypyc/test-data/irbuild-librt-strings.test |  6 +++---
 4 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/mypyc/lib-rt/librt_strings.c b/mypyc/lib-rt/librt_strings.c
index d403934b89154..086e5fd8dde5f 100644
--- a/mypyc/lib-rt/librt_strings.c
+++ b/mypyc/lib-rt/librt_strings.c
@@ -415,7 +415,6 @@ librt_strings_module_exec(PyObject *m)
         (void *)BytesWriter_append_internal,
         (void *)_grow_buffer,
         (void *)BytesWriter_type_internal,
-        (void *)BytesWriter_len_internal,
         (void *)BytesWriter_truncate_internal,
     };
     PyObject *c_api_object = PyCapsule_New((void *)librt_strings_api, "librt.strings._C_API", NULL);
diff --git a/mypyc/lib-rt/librt_strings.h b/mypyc/lib-rt/librt_strings.h
index ef5a43c654b7a..686453da36ec3 100644
--- a/mypyc/lib-rt/librt_strings.h
+++ b/mypyc/lib-rt/librt_strings.h
@@ -24,7 +24,7 @@ import_librt_strings(void)
 
 // Number of functions in the capsule API. If you add a new function, also increase
 // LIBRT_STRINGS_API_VERSION.
-#define LIBRT_STRINGS_API_LEN 9
+#define LIBRT_STRINGS_API_LEN 8
 
 static void *LibRTStrings_API[LIBRT_STRINGS_API_LEN];
 
@@ -46,8 +46,7 @@ typedef struct {
 #define LibRTStrings_BytesWriter_append_internal (*(char (*)(PyObject *source, uint8_t value)) LibRTStrings_API[4])
 #define LibRTStrings_ByteWriter_grow_buffer_internal (*(bool (*)(BytesWriterObject *obj, Py_ssize_t size)) LibRTStrings_API[5])
 #define LibRTStrings_BytesWriter_type_internal (*(PyTypeObject* (*)(void)) LibRTStrings_API[6])
-#define LibRTStrings_BytesWriter_len_internal (*(CPyTagged (*)(PyObject *self)) LibRTStrings_API[7])
-#define LibRTStrings_BytesWriter_truncate_internal (*(char (*)(PyObject *self, int64_t size)) LibRTStrings_API[8])
+#define LibRTStrings_BytesWriter_truncate_internal (*(char (*)(PyObject *self, int64_t size)) LibRTStrings_API[7])
 
 static int
 import_librt_strings(void)
@@ -134,6 +133,12 @@ CPyBytesWriter_Write(PyObject *obj, PyObject *value) {
     return CPY_NONE;
 }
 
+static inline CPyTagged
+CPyBytesWriter_Len(PyObject *obj) {
+    BytesWriterObject *self = (BytesWriterObject *)obj;
+    return (CPyTagged)self->len << 1;
+}
+
 #endif  // MYPYC_EXPERIMENTAL
 
 #endif  // LIBRT_STRINGS_H
diff --git a/mypyc/primitives/librt_strings_ops.py b/mypyc/primitives/librt_strings_ops.py
index 3545593f59cfe..062091d256814 100644
--- a/mypyc/primitives/librt_strings_ops.py
+++ b/mypyc/primitives/librt_strings_ops.py
@@ -66,7 +66,7 @@
     name="builtins.len",
     arg_types=[bytes_writer_rprimitive],
     return_type=short_int_rprimitive,
-    c_function_name="LibRTStrings_BytesWriter_len_internal",
+    c_function_name="CPyBytesWriter_Len",
     error_kind=ERR_NEVER,
     experimental=True,
     dependencies=[LIBRT_STRINGS],
diff --git a/mypyc/test-data/irbuild-librt-strings.test b/mypyc/test-data/irbuild-librt-strings.test
index 21aba382cdd8d..b61649844de22 100644
--- a/mypyc/test-data/irbuild-librt-strings.test
+++ b/mypyc/test-data/irbuild-librt-strings.test
@@ -29,9 +29,9 @@ def bytes_writer_basics():
 L0:
     r0 = LibRTStrings_BytesWriter_internal()
     b = r0
-    r1 = LibRTStrings_BytesWriter_append_internal(b, 1)
+    r1 = CPyBytesWriter_Append(b, 1)
     r2 = b'foo'
-    r3 = LibRTStrings_BytesWriter_write_internal(b, r2)
+    r3 = CPyBytesWriter_Write(b, r2)
     n = 4
     r4 = n & 1
     r5 = r4 == 0
@@ -55,6 +55,6 @@ def bytes_writer_len(b):
     r0 :: short_int
     r1 :: i64
 L0:
-    r0 = LibRTStrings_BytesWriter_len_internal(b)
+    r0 = CPyBytesWriter_Len(b)
     r1 = r0 >> 1
     return r1

From f9a6691f0f41dbd5dfc848e7e726aabdeba19e40 Mon Sep 17 00:00:00 2001
From: Jukka Lehtosalo <jukka.lehtosalo@iki.fi>
Date: Tue, 25 Nov 2025 17:20:32 +0000
Subject: [PATCH 3/9] Simplify len implementation

---
 mypyc/lib-rt/librt_strings.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mypyc/lib-rt/librt_strings.h b/mypyc/lib-rt/librt_strings.h
index 686453da36ec3..0069d0d7e8ad7 100644
--- a/mypyc/lib-rt/librt_strings.h
+++ b/mypyc/lib-rt/librt_strings.h
@@ -135,8 +135,7 @@ CPyBytesWriter_Write(PyObject *obj, PyObject *value) {
 
 static inline CPyTagged
 CPyBytesWriter_Len(PyObject *obj) {
-    BytesWriterObject *self = (BytesWriterObject *)obj;
-    return (CPyTagged)self->len << 1;
+    return (CPyTagged)((BytesWriterObject *)obj)->len << 1;
 }
 
 #endif  // MYPYC_EXPERIMENTAL

From 2fe8d43361945c66d18c609003d74c329409c45a Mon Sep 17 00:00:00 2001
From: Jukka Lehtosalo <jukka.lehtosalo@iki.fi>
Date: Mon, 8 Dec 2025 16:32:16 +0000
Subject: [PATCH 4/9] Move to a separate file

---
 mypyc/ir/deps.py                      |  1 +
 mypyc/lib-rt/byteswriter_extra_ops.c  | 27 ++++++++++++++
 mypyc/lib-rt/byteswriter_extra_ops.h  | 34 +++++++++++++++++
 mypyc/lib-rt/librt_strings.h          | 53 ---------------------------
 mypyc/primitives/librt_strings_ops.py | 10 +++--
 5 files changed, 68 insertions(+), 57 deletions(-)
 create mode 100644 mypyc/lib-rt/byteswriter_extra_ops.c
 create mode 100644 mypyc/lib-rt/byteswriter_extra_ops.h

diff --git a/mypyc/ir/deps.py b/mypyc/ir/deps.py
index b7747646628b1..9aee5d1b33e47 100644
--- a/mypyc/ir/deps.py
+++ b/mypyc/ir/deps.py
@@ -50,3 +50,4 @@ def get_header(self) -> str:
 LIBRT_BASE64: Final = Capsule("librt.base64")
 
 BYTES_EXTRA_OPS: Final = SourceDep("bytes_extra_ops.c")
+BYTES_WRITER_EXTRA_OPS: Final = SourceDep("byteswriter_extra_ops.c")
diff --git a/mypyc/lib-rt/byteswriter_extra_ops.c b/mypyc/lib-rt/byteswriter_extra_ops.c
new file mode 100644
index 0000000000000..337300c0adbfe
--- /dev/null
+++ b/mypyc/lib-rt/byteswriter_extra_ops.c
@@ -0,0 +1,27 @@
+#include "byteswriter_extra_ops.h"
+
+char CPyBytesWriter_Write(PyObject *obj, PyObject *value) {
+    BytesWriterObject *self = (BytesWriterObject *)obj;
+    const char *data;
+    Py_ssize_t size;
+    if (likely(PyBytes_Check(value))) {
+        data = PyBytes_AS_STRING(value);
+        size = PyBytes_GET_SIZE(value);
+    } else {
+        data = PyByteArray_AS_STRING(value);
+        size = PyByteArray_GET_SIZE(value);
+    }
+    // Write bytes content.
+    if (!CPyBytesWriter_EnsureSize(self, size))
+        return CPY_NONE_ERROR;
+    if (size < 8) {
+        char *p = self->buf + self->len;
+        for (Py_ssize_t i = 0; i < size; i++) {
+            p[i] = data[i];
+        }
+    } else {
+        memcpy(self->buf + self->len, data, size);
+    }
+    self->len += size;
+    return CPY_NONE;
+}
diff --git a/mypyc/lib-rt/byteswriter_extra_ops.h b/mypyc/lib-rt/byteswriter_extra_ops.h
new file mode 100644
index 0000000000000..09cd018d4e5f9
--- /dev/null
+++ b/mypyc/lib-rt/byteswriter_extra_ops.h
@@ -0,0 +1,34 @@
+#ifndef BYTESWRITER_EXTRA_OPS_H
+#define BYTESWRITER_EXTRA_OPS_H
+
+#include "librt_strings.h"
+
+static inline CPyTagged
+CPyBytesWriter_Len(PyObject *obj) {
+    return (CPyTagged)((BytesWriterObject *)obj)->len << 1;
+}
+
+static inline bool
+CPyBytesWriter_EnsureSize(BytesWriterObject *data, Py_ssize_t n) {
+    if (likely(data->capacity - data->len >= n)) {
+        return true;
+    } else {
+        return LibRTStrings_ByteWriter_grow_buffer_internal(data, n);
+    }
+}
+
+static inline char
+CPyBytesWriter_Append(PyObject *obj, uint8_t value) {
+    BytesWriterObject *self = (BytesWriterObject *)obj;
+    // Store length in a local variable to enable additional optimizations
+    Py_ssize_t len = self->len;
+    if (!CPyBytesWriter_EnsureSize(self, 1))
+        return CPY_NONE_ERROR;
+    self->buf[len] = value;
+    self->len = len + 1;
+    return CPY_NONE;
+}
+
+char CPyBytesWriter_Write(PyObject *obj, PyObject *value);
+
+#endif
diff --git a/mypyc/lib-rt/librt_strings.h b/mypyc/lib-rt/librt_strings.h
index 0069d0d7e8ad7..1176bcb3c25bf 100644
--- a/mypyc/lib-rt/librt_strings.h
+++ b/mypyc/lib-rt/librt_strings.h
@@ -85,59 +85,6 @@ static inline bool CPyBytesWriter_Check(PyObject *obj) {
     return Py_TYPE(obj) == LibRTStrings_BytesWriter_type_internal();
 }
 
-static inline bool
-CPyBytesWriter_EnsureSize(BytesWriterObject *data, Py_ssize_t n) {
-    if (likely(data->capacity - data->len >= n)) {
-        return true;
-    } else {
-        return LibRTStrings_ByteWriter_grow_buffer_internal(data, n);
-    }
-}
-
-static inline char
-CPyBytesWriter_Append(PyObject *obj, uint8_t value) {
-    BytesWriterObject *self = (BytesWriterObject *)obj;
-    // Store length in a local variable to enable additional optimizations
-    Py_ssize_t len = self->len;
-    if (!CPyBytesWriter_EnsureSize(self, 1))
-        return CPY_NONE_ERROR;
-    self->buf[len] = value;
-    self->len = len + 1;
-    return CPY_NONE;
-}
-
-static char
-CPyBytesWriter_Write(PyObject *obj, PyObject *value) {
-    BytesWriterObject *self = (BytesWriterObject *)obj;
-    const char *data;
-    Py_ssize_t size;
-    if (likely(PyBytes_Check(value))) {
-        data = PyBytes_AS_STRING(value);
-        size = PyBytes_GET_SIZE(value);
-    } else {
-        data = PyByteArray_AS_STRING(value);
-        size = PyByteArray_GET_SIZE(value);
-    }
-    // Write bytes content.
-    if (!CPyBytesWriter_EnsureSize(self, size))
-        return CPY_NONE_ERROR;
-    if (size < 8) {
-        char *p = self->buf + self->len;
-        for (Py_ssize_t i = 0; i < size; i++) {
-            p[i] = data[i];
-        }
-    } else {
-        memcpy(self->buf + self->len, data, size);
-    }
-    self->len += size;
-    return CPY_NONE;
-}
-
-static inline CPyTagged
-CPyBytesWriter_Len(PyObject *obj) {
-    return (CPyTagged)((BytesWriterObject *)obj)->len << 1;
-}
-
 #endif  // MYPYC_EXPERIMENTAL
 
 #endif  // LIBRT_STRINGS_H
diff --git a/mypyc/primitives/librt_strings_ops.py b/mypyc/primitives/librt_strings_ops.py
index 062091d256814..3b28388e770c8 100644
--- a/mypyc/primitives/librt_strings_ops.py
+++ b/mypyc/primitives/librt_strings_ops.py
@@ -1,6 +1,6 @@
 from typing import Final
 
-from mypyc.ir.deps import LIBRT_STRINGS
+from mypyc.ir.deps import LIBRT_STRINGS, BYTES_WRITER_EXTRA_OPS
 from mypyc.ir.ops import ERR_MAGIC, ERR_NEVER
 from mypyc.ir.rtypes import (
     KNOWN_NATIVE_TYPES,
@@ -41,7 +41,7 @@
     c_function_name="CPyBytesWriter_Write",
     error_kind=ERR_MAGIC,
     experimental=True,
-    dependencies=[LIBRT_STRINGS],
+    dependencies=[LIBRT_STRINGS, BYTES_WRITER_EXTRA_OPS],
 )
 
 method_op(
@@ -51,7 +51,7 @@
     c_function_name="CPyBytesWriter_Append",
     error_kind=ERR_MAGIC,
     experimental=True,
-    dependencies=[LIBRT_STRINGS],
+    dependencies=[LIBRT_STRINGS, BYTES_WRITER_EXTRA_OPS],
 )
 
 method_op(
@@ -60,6 +60,8 @@
     return_type=none_rprimitive,
     c_function_name="LibRTStrings_BytesWriter_truncate_internal",
     error_kind=ERR_MAGIC,
+    experimental=True,
+    dependencies=[LIBRT_STRINGS],
 )
 
 function_op(
@@ -69,5 +71,5 @@
     c_function_name="CPyBytesWriter_Len",
     error_kind=ERR_NEVER,
     experimental=True,
-    dependencies=[LIBRT_STRINGS],
+    dependencies=[LIBRT_STRINGS, BYTES_WRITER_EXTRA_OPS],
 )

From 3119162ae596b3957d1b7c9cf12c002803cad93e Mon Sep 17 00:00:00 2001
From: Jukka Lehtosalo <jukka.lehtosalo@iki.fi>
Date: Mon, 8 Dec 2025 16:35:38 +0000
Subject: [PATCH 5/9] Fix build

---
 mypyc/lib-rt/librt_strings.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mypyc/lib-rt/librt_strings.c b/mypyc/lib-rt/librt_strings.c
index 086e5fd8dde5f..d97d0f571f5b3 100644
--- a/mypyc/lib-rt/librt_strings.c
+++ b/mypyc/lib-rt/librt_strings.c
@@ -18,6 +18,8 @@
        ((BytesWriterObject *)data)->len += sizeof(type); \
     } while (0)
 
+#ifdef MYPYC_EXPERIMENTAL
+
 static PyTypeObject BytesWriterType;
 
 static bool
@@ -377,6 +379,8 @@ BytesWriter_len_internal(PyObject *self) {
     return writer->len << 1;
 }
 
+#endif
+
 static PyMethodDef librt_strings_module_methods[] = {
     {NULL, NULL, 0, NULL}
 };

From 513153b78c6a1b6b6e7da37a33184047b9e8edbc Mon Sep 17 00:00:00 2001
From: Jukka Lehtosalo <jukka.lehtosalo@iki.fi>
Date: Mon, 8 Dec 2025 16:36:44 +0000
Subject: [PATCH 6/9] Lint

---
 mypyc/primitives/librt_strings_ops.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mypyc/primitives/librt_strings_ops.py b/mypyc/primitives/librt_strings_ops.py
index 3b28388e770c8..1120254e24ae5 100644
--- a/mypyc/primitives/librt_strings_ops.py
+++ b/mypyc/primitives/librt_strings_ops.py
@@ -1,6 +1,6 @@
 from typing import Final
 
-from mypyc.ir.deps import LIBRT_STRINGS, BYTES_WRITER_EXTRA_OPS
+from mypyc.ir.deps import BYTES_WRITER_EXTRA_OPS, LIBRT_STRINGS
 from mypyc.ir.ops import ERR_MAGIC, ERR_NEVER
 from mypyc.ir.rtypes import (
     KNOWN_NATIVE_TYPES,

From eca46b4980e223f055a80140e3c3432e12f75db2 Mon Sep 17 00:00:00 2001
From: Jukka Lehtosalo <jukka.lehtosalo@iki.fi>
Date: Mon, 8 Dec 2025 16:42:03 +0000
Subject: [PATCH 7/9] Polish

---
 mypyc/lib-rt/byteswriter_extra_ops.c | 3 +++
 mypyc/lib-rt/librt_internal.c        | 2 --
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/mypyc/lib-rt/byteswriter_extra_ops.c b/mypyc/lib-rt/byteswriter_extra_ops.c
index 337300c0adbfe..76bf41045b742 100644
--- a/mypyc/lib-rt/byteswriter_extra_ops.c
+++ b/mypyc/lib-rt/byteswriter_extra_ops.c
@@ -1,3 +1,6 @@
+// Primitives related to librt.strings.BytesWriter that get linked statically
+// with compiled modules, instead of being called via a capsule.
+
 #include "byteswriter_extra_ops.h"
 
 char CPyBytesWriter_Write(PyObject *obj, PyObject *value) {
diff --git a/mypyc/lib-rt/librt_internal.c b/mypyc/lib-rt/librt_internal.c
index fe18c541c11fc..9c57d8bef72c9 100644
--- a/mypyc/lib-rt/librt_internal.c
+++ b/mypyc/lib-rt/librt_internal.c
@@ -27,8 +27,6 @@
 #define LONG_INT_TRAILER 15
 
 #define CPY_BOOL_ERROR 2
-#define CPY_NONE_ERROR 2
-#define CPY_NONE 1
 
 #define _CHECK_READ_BUFFER(data, err)  if (unlikely(_check_read_buffer(data) == CPY_NONE_ERROR)) \
                                            return err;

From 86037229f4050b4b4cdffbad389802e80e06e7e1 Mon Sep 17 00:00:00 2001
From: Jukka Lehtosalo <jukka.lehtosalo@iki.fi>
Date: Mon, 8 Dec 2025 17:25:05 +0000
Subject: [PATCH 8/9] Update capsule version

---
 mypyc/lib-rt/librt_strings.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mypyc/lib-rt/librt_strings.h b/mypyc/lib-rt/librt_strings.h
index 1176bcb3c25bf..e619435f52920 100644
--- a/mypyc/lib-rt/librt_strings.h
+++ b/mypyc/lib-rt/librt_strings.h
@@ -15,12 +15,12 @@ import_librt_strings(void)
 // ABI version -- only an exact match is compatible. This will only be changed in
 // very exceptional cases (likely never) due to strict backward compatibility
 // requirements.
-#define LIBRT_STRINGS_ABI_VERSION 0
+#define LIBRT_STRINGS_ABI_VERSION 1
 
 // API version -- more recent versions must maintain backward compatibility, i.e.
 // we can add new features but not remove or change existing features (unless
 // ABI version is changed, but see the comment above).
- #define LIBRT_STRINGS_API_VERSION 1
+ #define LIBRT_STRINGS_API_VERSION 2
 
 // Number of functions in the capsule API. If you add a new function, also increase
 // LIBRT_STRINGS_API_VERSION.

From 51f01c6dae12c1875591131e6a7177d3e6da4293 Mon Sep 17 00:00:00 2001
From: Jukka Lehtosalo <jukka.lehtosalo@iki.fi>
Date: Mon, 8 Dec 2025 17:25:13 +0000
Subject: [PATCH 9/9] Add comment

---
 mypyc/lib-rt/byteswriter_extra_ops.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mypyc/lib-rt/byteswriter_extra_ops.c b/mypyc/lib-rt/byteswriter_extra_ops.c
index 76bf41045b742..03827bf54fea7 100644
--- a/mypyc/lib-rt/byteswriter_extra_ops.c
+++ b/mypyc/lib-rt/byteswriter_extra_ops.c
@@ -18,6 +18,7 @@ char CPyBytesWriter_Write(PyObject *obj, PyObject *value) {
     if (!CPyBytesWriter_EnsureSize(self, size))
         return CPY_NONE_ERROR;
     if (size < 8) {
+        // Loop tends to be faster for small sizes
         char *p = self->buf + self->len;
         for (Py_ssize_t i = 0; i < size; i++) {
             p[i] = data[i];