1 files changed, 73 insertions, 0 deletions

diff --git a/gl/m4/ungetc.m4 b/gl/m4/ungetc.m4
new file mode 100644
index 00000000..8977a346
--- /dev/null
+++ b/gl/m4/ungetc.m4
@@ -0,0 +1,73 @@
+# ungetc.m4 serial 10
+dnl Copyright (C) 2009-2023 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN_ONCE([gl_FUNC_UNGETC_WORKS],
+[
+  AC_REQUIRE([AC_PROG_CC])
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+
+  AC_CACHE_CHECK([whether ungetc works on arbitrary bytes],
+    [gl_cv_func_ungetc_works],
+    [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+#include <stdio.h>
+      ]], [[FILE *f;
+            if (!(f = fopen ("conftest.tmp", "w+")))
+              return 1;
+            if (fputs ("abc", f) < 0)
+              { fclose (f); return 2; }
+            rewind (f);
+            if (fgetc (f) != 'a')
+              { fclose (f); return 3; }
+            if (fgetc (f) != 'b')
+              { fclose (f); return 4; }
+            if (ungetc ('d', f) != 'd')
+              { fclose (f); return 5; }
+            if (ftell (f) != 1)
+              { fclose (f); return 6; }
+            if (fgetc (f) != 'd')
+              { fclose (f); return 7; }
+            if (ftell (f) != 2)
+              { fclose (f); return 8; }
+            if (fseek (f, 0, SEEK_CUR) != 0)
+              { fclose (f); return 9; }
+            if (ftell (f) != 2)
+              { fclose (f); return 10; }
+            if (fgetc (f) != 'c')
+              { fclose (f); return 11; }
+            fclose (f);
+            remove ("conftest.tmp");
+          ]])],
+        [gl_cv_func_ungetc_works=yes], [gl_cv_func_ungetc_works=no],
+        [case "$host_os" in
+                          # Guess yes on glibc systems.
+           *-gnu* | gnu*) gl_cv_func_ungetc_works="guessing yes" ;;
+                          # Guess yes on musl systems.
+           *-musl*)       gl_cv_func_ungetc_works="guessing yes" ;;
+                          # Guess yes on bionic systems.
+           *-android*)    gl_cv_func_ungetc_works="guessing yes" ;;
+                          # Guess yes on native Windows.
+           mingw*)        gl_cv_func_ungetc_works="guessing yes" ;;
+                          # If we don't know, obey --enable-cross-guesses.
+           *)             gl_cv_func_ungetc_works="$gl_cross_guess_normal" ;;
+         esac
+        ])
+    ])
+  gl_ftello_broken_after_ungetc=no
+  case "$gl_cv_func_ungetc_works" in
+    *yes) ;;
+    *)
+      dnl On macOS >= 10.15, where the above program fails with exit code 6,
+      dnl we fix it through an ftello override.
+      case "$host_os" in
+        darwin*) gl_ftello_broken_after_ungetc=yes ;;
+        *)
+          AC_DEFINE([FUNC_UNGETC_BROKEN], [1],
+            [Define to 1 if ungetc is broken when used on arbitrary bytes.])
+          ;;
+      esac
+      ;;
+  esac
+])