From adfb42bfa6baaa8c4190a162339d406e928b432a Mon Sep 17 00:00:00 2001
From: Colin Leroy-Mira <colin@colino.net>
Date: Wed, 1 Jan 2025 13:23:57 +0100
Subject: [PATCH] Rewrite rewind in assembly

---
 libsrc/common/rewind.c | 25 -------------------
 libsrc/common/rewind.s | 35 ++++++++++++++++++++++++++
 test/ref/test_rewind.c | 56 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 91 insertions(+), 25 deletions(-)
 delete mode 100644 libsrc/common/rewind.c
 create mode 100644 libsrc/common/rewind.s
 create mode 100644 test/ref/test_rewind.c

diff --git a/libsrc/common/rewind.c b/libsrc/common/rewind.c
deleted file mode 100644
index 333230b74..000000000
--- a/libsrc/common/rewind.c
+++ /dev/null
@@ -1,25 +0,0 @@
-/*
-** rewind.c
-**
-** Christian Groessler, 07-Aug-2000
-*/
-
-
-
-#include <stdio.h>
-
-
-
-/*****************************************************************************/
-/*                                   Code                                    */
-/*****************************************************************************/
-
-
-
-void __fastcall__ rewind (FILE* f)
-{
-    fseek(f, 0L, SEEK_SET);
-    clearerr(f);
-}
-
-
diff --git a/libsrc/common/rewind.s b/libsrc/common/rewind.s
new file mode 100644
index 000000000..e7013505c
--- /dev/null
+++ b/libsrc/common/rewind.s
@@ -0,0 +1,35 @@
+;
+; Colin Leroy-Mira <colin@colino.net>
+;
+; void __fastcall__ rewind (FILE* f)
+; /* Rewind a file */
+;
+
+        .export         _rewind
+
+        .import         _fseek, _clearerr
+        .import         pushax, pushl0, popax
+
+        .include        "stdio.inc"
+
+
+; ------------------------------------------------------------------------
+; Code
+
+.proc   _rewind
+
+        ; Push f twice (once for fseek, once for clearerr later)
+        jsr     pushax
+        jsr     pushax
+
+        ; Push offset (long) zero
+        jsr     pushl0
+
+        lda     #SEEK_SET
+        jsr     _fseek
+
+        ; Clear error
+        jsr     popax
+        jmp     _clearerr
+
+.endproc
diff --git a/test/ref/test_rewind.c b/test/ref/test_rewind.c
new file mode 100644
index 000000000..80fe08ce1
--- /dev/null
+++ b/test/ref/test_rewind.c
@@ -0,0 +1,56 @@
+/*
+  !!DESCRIPTION!! fgets test
+  !!LICENCE!!     Public domain
+*/
+
+#include "common.h"
+
+#include <ctype.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+FILE *in;
+char bufA[32];
+char bufB[32];
+
+#define INFILE   "cf.in"
+
+int main(int argc,char **argv)
+{
+    static int r;
+
+    in = fopen(INFILE, "rb");
+    if (in == NULL) {
+        return EXIT_FAILURE;
+    }
+
+    r = fread(bufA, 1, sizeof(bufA), in);
+
+    if (r == 0) {
+      printf("Error: could not read.\n");
+      return EXIT_FAILURE;
+    }
+    fwrite(bufA, 1, r, stdout);
+
+    rewind(in);
+    printf("rewind.\n");
+    r = fread(bufB, 1, sizeof(bufB), in);
+
+    if (r == 0) {
+      printf("Error: could not re-read.\n");
+      return EXIT_FAILURE;
+    }
+    fwrite(bufB, 1, r, stdout);
+
+    fclose(in);
+
+    if (memcmp(bufA, bufB, sizeof(bufA))) {
+      printf("reads differ.\n");
+      return EXIT_FAILURE;
+    }
+
+    return 0;
+}