diff --git a/internal/cgen/base/io-private.h b/internal/cgen/base/io-private.h
index 1894934..3de0a0c 100644
--- a/internal/cgen/base/io-private.h
+++ b/internal/cgen/base/io-private.h
@@ -16,12 +16,6 @@
 
 // ---------------- I/O
 
-static inline bool  //
-wuffs_base__io_buffer__is_valid(wuffs_base__io_buffer buf) {
-  return (buf.data.ptr || (buf.data.len == 0)) &&
-         (buf.data.len >= buf.meta.wi) && (buf.meta.wi >= buf.meta.ri);
-}
-
 static inline uint64_t  //
 wuffs_base__io__count_since(uint64_t mark, uint64_t index) {
   if (index >= mark) {
@@ -52,30 +46,6 @@
          (buf->data.ptr + buf->meta.wi == o.private_impl.limit);
 }
 
-static inline bool  //
-wuffs_base__io_reader__is_valid(wuffs_base__io_reader o) {
-  wuffs_base__io_buffer* buf = o.private_impl.buf;
-  // Note: if making this function public (i.e. moving it to base-header.h), it
-  // also needs to allow NULL (i.e. implicit, callee-calculated) mark/limit.
-  return buf ? ((buf->data.ptr <= o.private_impl.mark) &&
-                (o.private_impl.mark <= o.private_impl.limit) &&
-                (o.private_impl.limit <= buf->data.ptr + buf->data.len))
-             : ((o.private_impl.mark == NULL) &&
-                (o.private_impl.limit == NULL));
-}
-
-static inline bool  //
-wuffs_base__io_writer__is_valid(wuffs_base__io_writer o) {
-  wuffs_base__io_buffer* buf = o.private_impl.buf;
-  // Note: if making this function public (i.e. moving it to base-header.h), it
-  // also needs to allow NULL (i.e. implicit, callee-calculated) mark/limit.
-  return buf ? ((buf->data.ptr <= o.private_impl.mark) &&
-                (o.private_impl.mark <= o.private_impl.limit) &&
-                (o.private_impl.limit <= buf->data.ptr + buf->data.len))
-             : ((o.private_impl.mark == NULL) &&
-                (o.private_impl.limit == NULL));
-}
-
 static inline uint32_t  //
 wuffs_base__io_writer__copy_n_from_history(uint8_t** ptr_iop_w,
                                            uint8_t* io0_w,
diff --git a/internal/cgen/data.go b/internal/cgen/data.go
index dd3d0cd..f122f14 100644
--- a/internal/cgen/data.go
+++ b/internal/cgen/data.go
@@ -163,14 +163,13 @@
 	""
 
 const baseIOPrivateH = "" +
-	"// ---------------- I/O\n\nstatic inline bool  //\nwuffs_base__io_buffer__is_valid(wuffs_base__io_buffer buf) {\n  return (buf.data.ptr || (buf.data.len == 0)) &&\n         (buf.data.len >= buf.meta.wi) && (buf.meta.wi >= buf.meta.ri);\n}\n\nstatic inline uint64_t  //\nwuffs_base__io__count_since(uint64_t mark, uint64_t index) {\n  if (index >= mark) {\n    return index - mark;\n  }\n  return 0;\n}\n\nstatic inline wuffs_base__slice_u8  //\nwuffs_base__io__since(uint64_t mark, uint64_t index, uint8_t* ptr) {\n  if (index >= mark) {\n    return wuffs_base__make_slice_u8(ptr + mark, index - mark);\n  }\n  return wuffs_base__make_slice_u8(NULL, 0);\n}\n\n// TODO: wuffs_base__io_reader__is_eof is no longer used by Wuffs per se, but\n// it might be handy to programs that use Wuffs. Either delete it, or promote\n// it to the public API.\n//\n// If making this function public (i.e. moving it to base-header.h), it also\n// needs to allow NULL (i.e. implicit, callee-calculated) mark/limit.\n\nstatic inline bool  //\nwuffs_base__io_reader__is_eof(wuf" +
-	"fs_base__io_reader o) {\n  wuffs_base__io_buffer* buf = o.private_impl.buf;\n  return buf && buf->meta.closed &&\n         (buf->data.ptr + buf->meta.wi == o.private_impl.limit);\n}\n\nstatic inline bool  //\nwuffs_base__io_reader__is_valid(wuffs_base__io_reader o) {\n  wuffs_base__io_buffer* buf = o.private_impl.buf;\n  // Note: if making this function public (i.e. moving it to base-header.h), it\n  // also needs to allow NULL (i.e. implicit, callee-calculated) mark/limit.\n  return buf ? ((buf->data.ptr <= o.private_impl.mark) &&\n                (o.private_impl.mark <= o.private_impl.limit) &&\n                (o.private_impl.limit <= buf->data.ptr + buf->data.len))\n             : ((o.private_impl.mark == NULL) &&\n                (o.private_impl.limit == NULL));\n}\n\nstatic inline bool  //\nwuffs_base__io_writer__is_valid(wuffs_base__io_writer o) {\n  wuffs_base__io_buffer* buf = o.private_impl.buf;\n  // Note: if making this function public (i.e. moving it to base-header.h), it\n  // also needs to allow NULL (i.e. implicit," +
-	" callee-calculated) mark/limit.\n  return buf ? ((buf->data.ptr <= o.private_impl.mark) &&\n                (o.private_impl.mark <= o.private_impl.limit) &&\n                (o.private_impl.limit <= buf->data.ptr + buf->data.len))\n             : ((o.private_impl.mark == NULL) &&\n                (o.private_impl.limit == NULL));\n}\n\nstatic inline uint32_t  //\nwuffs_base__io_writer__copy_n_from_history(uint8_t** ptr_iop_w,\n                                           uint8_t* io0_w,\n                                           uint8_t* io1_w,\n                                           uint32_t length,\n                                           uint32_t distance) {\n  if (!distance) {\n    return 0;\n  }\n  uint8_t* p = *ptr_iop_w;\n  if ((size_t)(p - io0_w) < (size_t)(distance)) {\n    return 0;\n  }\n  uint8_t* q = p - distance;\n  size_t n = (size_t)(io1_w - p);\n  if ((size_t)(length) > n) {\n    length = (uint32_t)(n);\n  } else {\n    n = (size_t)(length);\n  }\n  // TODO: unrolling by 3 seems best for the std/deflate benchmarks," +
-	" but that\n  // is mostly because 3 is the minimum length for the deflate format. This\n  // function implementation shouldn't overfit to that one format. Perhaps the\n  // copy_n_from_history Wuffs method should also take an unroll hint argument,\n  // and the cgen can look if that argument is the constant expression '3'.\n  //\n  // See also wuffs_base__io_writer__copy_n_from_history_fast below.\n  //\n  // Alternatively, or additionally, have a sloppy_copy_n_from_history method\n  // that copies 8 bytes at a time, possibly writing more than length bytes?\n  for (; n >= 3; n -= 3) {\n    *p++ = *q++;\n    *p++ = *q++;\n    *p++ = *q++;\n  }\n  for (; n; n--) {\n    *p++ = *q++;\n  }\n  *ptr_iop_w = p;\n  return length;\n}\n\n// wuffs_base__io_writer__copy_n_from_history_fast is like the\n// wuffs_base__io_writer__copy_n_from_history function above, but has stronger\n// pre-conditions. The caller needs to prove that:\n//  - distance >  0\n//  - distance <= (*ptr_iop_w - io0_w)\n//  - length   <= (io1_w      - *ptr_iop_w)\nstatic inline" +
-	" uint32_t  //\nwuffs_base__io_writer__copy_n_from_history_fast(uint8_t** ptr_iop_w,\n                                                uint8_t* io0_w,\n                                                uint8_t* io1_w,\n                                                uint32_t length,\n                                                uint32_t distance) {\n  uint8_t* p = *ptr_iop_w;\n  uint8_t* q = p - distance;\n  uint32_t n = length;\n  for (; n >= 3; n -= 3) {\n    *p++ = *q++;\n    *p++ = *q++;\n    *p++ = *q++;\n  }\n  for (; n; n--) {\n    *p++ = *q++;\n  }\n  *ptr_iop_w = p;\n  return length;\n}\n\nstatic inline uint32_t  //\nwuffs_base__io_writer__copy_n_from_reader(uint8_t** ptr_iop_w,\n                                          uint8_t* io1_w,\n                                          uint32_t length,\n                                          uint8_t** ptr_iop_r,\n                                          uint8_t* io1_r) {\n  uint8_t* iop_w = *ptr_iop_w;\n  size_t n = length;\n  if (n > ((size_t)(io1_w - iop_w))) {\n    n = (size_t)(io" +
-	"1_w - iop_w);\n  }\n  uint8_t* iop_r = *ptr_iop_r;\n  if (n > ((size_t)(io1_r - iop_r))) {\n    n = (size_t)(io1_r - iop_r);\n  }\n  if (n > 0) {\n    memmove(iop_w, iop_r, n);\n    *ptr_iop_w += n;\n    *ptr_iop_r += n;\n  }\n  return (uint32_t)(n);\n}\n\nstatic inline uint64_t  //\nwuffs_base__io_writer__copy_from_slice(uint8_t** ptr_iop_w,\n                                       uint8_t* io1_w,\n                                       wuffs_base__slice_u8 src) {\n  uint8_t* iop_w = *ptr_iop_w;\n  size_t n = src.len;\n  if (n > ((size_t)(io1_w - iop_w))) {\n    n = (size_t)(io1_w - iop_w);\n  }\n  if (n > 0) {\n    memmove(iop_w, src.ptr, n);\n    *ptr_iop_w += n;\n  }\n  return (uint64_t)(n);\n}\n\nstatic inline uint32_t  //\nwuffs_base__io_writer__copy_n_from_slice(uint8_t** ptr_iop_w,\n                                         uint8_t* io1_w,\n                                         uint32_t length,\n                                         wuffs_base__slice_u8 src) {\n  uint8_t* iop_w = *ptr_iop_w;\n  size_t n = src.len;\n  if (n > length) " +
-	"{\n    n = length;\n  }\n  if (n > ((size_t)(io1_w - iop_w))) {\n    n = (size_t)(io1_w - iop_w);\n  }\n  if (n > 0) {\n    memmove(iop_w, src.ptr, n);\n    *ptr_iop_w += n;\n  }\n  return (uint32_t)(n);\n}\n\nstatic inline wuffs_base__empty_struct  //\nwuffs_base__io_reader__set(wuffs_base__io_reader* o,\n                           wuffs_base__io_buffer* b,\n                           uint8_t** ptr_iop_r,\n                           uint8_t** ptr_io1_r,\n                           wuffs_base__slice_u8 data) {\n  b->data = data;\n  b->meta.wi = data.len;\n  b->meta.ri = 0;\n  b->meta.pos = 0;\n  b->meta.closed = false;\n\n  o->private_impl.buf = b;\n  o->private_impl.mark = data.ptr;\n  o->private_impl.limit = data.ptr + data.len;\n  *ptr_iop_r = data.ptr;\n  *ptr_io1_r = data.ptr + data.len;\n\n  wuffs_base__empty_struct ret;\n  ret.private_impl = 0;\n  return ret;\n}\n\nstatic inline wuffs_base__slice_u8  //\nwuffs_base__io_reader__take(uint8_t** ptr_iop_r, uint8_t* io1_r, uint64_t n) {\n  if (n <= ((size_t)(io1_r - *ptr_iop_r))) {\n    uint8_t*" +
-	" p = *ptr_iop_r;\n    *ptr_iop_r += n;\n    return wuffs_base__make_slice_u8(p, n);\n  }\n  return wuffs_base__make_slice_u8(NULL, 0);\n}\n\nstatic inline wuffs_base__empty_struct  //\nwuffs_base__io_writer__set(wuffs_base__io_writer* o,\n                           wuffs_base__io_buffer* b,\n                           uint8_t** ptr_iop_w,\n                           uint8_t** ptr_io1_w,\n                           wuffs_base__slice_u8 data) {\n  b->data = data;\n  b->meta.wi = 0;\n  b->meta.ri = 0;\n  b->meta.pos = 0;\n  b->meta.closed = false;\n\n  o->private_impl.buf = b;\n  o->private_impl.mark = data.ptr;\n  o->private_impl.limit = data.ptr + data.len;\n  *ptr_iop_w = data.ptr;\n  *ptr_io1_w = data.ptr + data.len;\n\n  wuffs_base__empty_struct ret;\n  ret.private_impl = 0;\n  return ret;\n}\n\n" +
+	"// ---------------- I/O\n\nstatic inline uint64_t  //\nwuffs_base__io__count_since(uint64_t mark, uint64_t index) {\n  if (index >= mark) {\n    return index - mark;\n  }\n  return 0;\n}\n\nstatic inline wuffs_base__slice_u8  //\nwuffs_base__io__since(uint64_t mark, uint64_t index, uint8_t* ptr) {\n  if (index >= mark) {\n    return wuffs_base__make_slice_u8(ptr + mark, index - mark);\n  }\n  return wuffs_base__make_slice_u8(NULL, 0);\n}\n\n// TODO: wuffs_base__io_reader__is_eof is no longer used by Wuffs per se, but\n// it might be handy to programs that use Wuffs. Either delete it, or promote\n// it to the public API.\n//\n// If making this function public (i.e. moving it to base-header.h), it also\n// needs to allow NULL (i.e. implicit, callee-calculated) mark/limit.\n\nstatic inline bool  //\nwuffs_base__io_reader__is_eof(wuffs_base__io_reader o) {\n  wuffs_base__io_buffer* buf = o.private_impl.buf;\n  return buf && buf->meta.closed &&\n         (buf->data.ptr + buf->meta.wi == o.private_impl.limit);\n}\n\nstatic inline uint32_t  //\nwuf" +
+	"fs_base__io_writer__copy_n_from_history(uint8_t** ptr_iop_w,\n                                           uint8_t* io0_w,\n                                           uint8_t* io1_w,\n                                           uint32_t length,\n                                           uint32_t distance) {\n  if (!distance) {\n    return 0;\n  }\n  uint8_t* p = *ptr_iop_w;\n  if ((size_t)(p - io0_w) < (size_t)(distance)) {\n    return 0;\n  }\n  uint8_t* q = p - distance;\n  size_t n = (size_t)(io1_w - p);\n  if ((size_t)(length) > n) {\n    length = (uint32_t)(n);\n  } else {\n    n = (size_t)(length);\n  }\n  // TODO: unrolling by 3 seems best for the std/deflate benchmarks, but that\n  // is mostly because 3 is the minimum length for the deflate format. This\n  // function implementation shouldn't overfit to that one format. Perhaps the\n  // copy_n_from_history Wuffs method should also take an unroll hint argument,\n  // and the cgen can look if that argument is the constant expression '3'.\n  //\n  // See also wuffs_base__io_writ" +
+	"er__copy_n_from_history_fast below.\n  //\n  // Alternatively, or additionally, have a sloppy_copy_n_from_history method\n  // that copies 8 bytes at a time, possibly writing more than length bytes?\n  for (; n >= 3; n -= 3) {\n    *p++ = *q++;\n    *p++ = *q++;\n    *p++ = *q++;\n  }\n  for (; n; n--) {\n    *p++ = *q++;\n  }\n  *ptr_iop_w = p;\n  return length;\n}\n\n// wuffs_base__io_writer__copy_n_from_history_fast is like the\n// wuffs_base__io_writer__copy_n_from_history function above, but has stronger\n// pre-conditions. The caller needs to prove that:\n//  - distance >  0\n//  - distance <= (*ptr_iop_w - io0_w)\n//  - length   <= (io1_w      - *ptr_iop_w)\nstatic inline uint32_t  //\nwuffs_base__io_writer__copy_n_from_history_fast(uint8_t** ptr_iop_w,\n                                                uint8_t* io0_w,\n                                                uint8_t* io1_w,\n                                                uint32_t length,\n                                                uint32_t distance) {\n  uint8_t* p =" +
+	" *ptr_iop_w;\n  uint8_t* q = p - distance;\n  uint32_t n = length;\n  for (; n >= 3; n -= 3) {\n    *p++ = *q++;\n    *p++ = *q++;\n    *p++ = *q++;\n  }\n  for (; n; n--) {\n    *p++ = *q++;\n  }\n  *ptr_iop_w = p;\n  return length;\n}\n\nstatic inline uint32_t  //\nwuffs_base__io_writer__copy_n_from_reader(uint8_t** ptr_iop_w,\n                                          uint8_t* io1_w,\n                                          uint32_t length,\n                                          uint8_t** ptr_iop_r,\n                                          uint8_t* io1_r) {\n  uint8_t* iop_w = *ptr_iop_w;\n  size_t n = length;\n  if (n > ((size_t)(io1_w - iop_w))) {\n    n = (size_t)(io1_w - iop_w);\n  }\n  uint8_t* iop_r = *ptr_iop_r;\n  if (n > ((size_t)(io1_r - iop_r))) {\n    n = (size_t)(io1_r - iop_r);\n  }\n  if (n > 0) {\n    memmove(iop_w, iop_r, n);\n    *ptr_iop_w += n;\n    *ptr_iop_r += n;\n  }\n  return (uint32_t)(n);\n}\n\nstatic inline uint64_t  //\nwuffs_base__io_writer__copy_from_slice(uint8_t** ptr_iop_w,\n                             " +
+	"          uint8_t* io1_w,\n                                       wuffs_base__slice_u8 src) {\n  uint8_t* iop_w = *ptr_iop_w;\n  size_t n = src.len;\n  if (n > ((size_t)(io1_w - iop_w))) {\n    n = (size_t)(io1_w - iop_w);\n  }\n  if (n > 0) {\n    memmove(iop_w, src.ptr, n);\n    *ptr_iop_w += n;\n  }\n  return (uint64_t)(n);\n}\n\nstatic inline uint32_t  //\nwuffs_base__io_writer__copy_n_from_slice(uint8_t** ptr_iop_w,\n                                         uint8_t* io1_w,\n                                         uint32_t length,\n                                         wuffs_base__slice_u8 src) {\n  uint8_t* iop_w = *ptr_iop_w;\n  size_t n = src.len;\n  if (n > length) {\n    n = length;\n  }\n  if (n > ((size_t)(io1_w - iop_w))) {\n    n = (size_t)(io1_w - iop_w);\n  }\n  if (n > 0) {\n    memmove(iop_w, src.ptr, n);\n    *ptr_iop_w += n;\n  }\n  return (uint32_t)(n);\n}\n\nstatic inline wuffs_base__empty_struct  //\nwuffs_base__io_reader__set(wuffs_base__io_reader* o,\n                           wuffs_base__io_buffer* b,\n             " +
+	"              uint8_t** ptr_iop_r,\n                           uint8_t** ptr_io1_r,\n                           wuffs_base__slice_u8 data) {\n  b->data = data;\n  b->meta.wi = data.len;\n  b->meta.ri = 0;\n  b->meta.pos = 0;\n  b->meta.closed = false;\n\n  o->private_impl.buf = b;\n  o->private_impl.mark = data.ptr;\n  o->private_impl.limit = data.ptr + data.len;\n  *ptr_iop_r = data.ptr;\n  *ptr_io1_r = data.ptr + data.len;\n\n  wuffs_base__empty_struct ret;\n  ret.private_impl = 0;\n  return ret;\n}\n\nstatic inline wuffs_base__slice_u8  //\nwuffs_base__io_reader__take(uint8_t** ptr_iop_r, uint8_t* io1_r, uint64_t n) {\n  if (n <= ((size_t)(io1_r - *ptr_iop_r))) {\n    uint8_t* p = *ptr_iop_r;\n    *ptr_iop_r += n;\n    return wuffs_base__make_slice_u8(p, n);\n  }\n  return wuffs_base__make_slice_u8(NULL, 0);\n}\n\nstatic inline wuffs_base__empty_struct  //\nwuffs_base__io_writer__set(wuffs_base__io_writer* o,\n                           wuffs_base__io_buffer* b,\n                           uint8_t** ptr_iop_w,\n                           u" +
+	"int8_t** ptr_io1_w,\n                           wuffs_base__slice_u8 data) {\n  b->data = data;\n  b->meta.wi = 0;\n  b->meta.ri = 0;\n  b->meta.pos = 0;\n  b->meta.closed = false;\n\n  o->private_impl.buf = b;\n  o->private_impl.mark = data.ptr;\n  o->private_impl.limit = data.ptr + data.len;\n  *ptr_iop_w = data.ptr;\n  *ptr_io1_w = data.ptr + data.len;\n\n  wuffs_base__empty_struct ret;\n  ret.private_impl = 0;\n  return ret;\n}\n\n" +
 	"" +
 	"// ---------------- I/O (Utility)\n\n#define wuffs_base__utility__null_io_reader wuffs_base__null_io_reader\n#define wuffs_base__utility__null_io_writer wuffs_base__null_io_writer\n" +
 	""
diff --git a/release/c/wuffs-unsupported-snapshot.c b/release/c/wuffs-unsupported-snapshot.c
index 6fdcb40..63e0e42 100644
--- a/release/c/wuffs-unsupported-snapshot.c
+++ b/release/c/wuffs-unsupported-snapshot.c
@@ -4520,12 +4520,6 @@
 
 // ---------------- I/O
 
-static inline bool  //
-wuffs_base__io_buffer__is_valid(wuffs_base__io_buffer buf) {
-  return (buf.data.ptr || (buf.data.len == 0)) &&
-         (buf.data.len >= buf.meta.wi) && (buf.meta.wi >= buf.meta.ri);
-}
-
 static inline uint64_t  //
 wuffs_base__io__count_since(uint64_t mark, uint64_t index) {
   if (index >= mark) {
@@ -4556,30 +4550,6 @@
          (buf->data.ptr + buf->meta.wi == o.private_impl.limit);
 }
 
-static inline bool  //
-wuffs_base__io_reader__is_valid(wuffs_base__io_reader o) {
-  wuffs_base__io_buffer* buf = o.private_impl.buf;
-  // Note: if making this function public (i.e. moving it to base-header.h), it
-  // also needs to allow NULL (i.e. implicit, callee-calculated) mark/limit.
-  return buf ? ((buf->data.ptr <= o.private_impl.mark) &&
-                (o.private_impl.mark <= o.private_impl.limit) &&
-                (o.private_impl.limit <= buf->data.ptr + buf->data.len))
-             : ((o.private_impl.mark == NULL) &&
-                (o.private_impl.limit == NULL));
-}
-
-static inline bool  //
-wuffs_base__io_writer__is_valid(wuffs_base__io_writer o) {
-  wuffs_base__io_buffer* buf = o.private_impl.buf;
-  // Note: if making this function public (i.e. moving it to base-header.h), it
-  // also needs to allow NULL (i.e. implicit, callee-calculated) mark/limit.
-  return buf ? ((buf->data.ptr <= o.private_impl.mark) &&
-                (o.private_impl.mark <= o.private_impl.limit) &&
-                (o.private_impl.limit <= buf->data.ptr + buf->data.len))
-             : ((o.private_impl.mark == NULL) &&
-                (o.private_impl.limit == NULL));
-}
-
 static inline uint32_t  //
 wuffs_base__io_writer__copy_n_from_history(uint8_t** ptr_iop_w,
                                            uint8_t* io0_w,