From c5c92d9615cc8eea6181c82a4cf103fa22f64b13 Mon Sep 17 00:00:00 2001
From: Jonas 'Sortie' Termansen <sortie@maxsi.org>
Date: Tue, 29 May 2012 00:04:57 +0200
Subject: [PATCH] Added ungetc(3).

---
 libmaxsi/decl/FILE.h     |  3 +++
 libmaxsi/file.c          | 24 +++++++++++++++++++++++-
 libmaxsi/include/stdio.h |  2 +-
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/libmaxsi/decl/FILE.h b/libmaxsi/decl/FILE.h
index 13d5ef83..ba6c5195 100644
--- a/libmaxsi/decl/FILE.h
+++ b/libmaxsi/decl/FILE.h
@@ -6,6 +6,7 @@
 #define _FILE_LAST_WRITE (1<<2)
 #define _FILE_LAST_READ (1<<3)
 #define _FILE_AUTO_LOCK (1<<4)
+#define _FILE_MAX_PUSHBACK 8
 typedef struct _FILE
 {
 	/* This is non-standard, but useful. If you allocate your own FILE and
@@ -31,5 +32,7 @@ typedef struct _FILE
 	struct _FILE* next;
 	int flags;
 	size_t bufferused;
+	size_t numpushedback;
+	unsigned char pushedback[_FILE_MAX_PUSHBACK];
 } FILE;
 #endif
diff --git a/libmaxsi/file.c b/libmaxsi/file.c
index a13bc439..4307e5ac 100644
--- a/libmaxsi/file.c
+++ b/libmaxsi/file.c
@@ -52,6 +52,18 @@ void funregister(FILE* fp)
 
 size_t fread(void* ptr, size_t size, size_t nmemb, FILE* fp)
 {
+	if ( fp->numpushedback && size != 1 ) { errno = ENOSYS; return 0; }
+	if ( fp->numpushedback && nmemb )
+	{
+		unsigned char* buf = (unsigned char*) ptr;
+		size_t amount = nmemb < fp->numpushedback ? nmemb : fp->numpushedback;
+		for ( size_t i = 0; i < amount; i++ )
+		{
+			buf[i] = fp->pushedback[--(fp->numpushedback)];
+		}
+		if ( nmemb <= amount ) { return nmemb; }
+		return amount + fread(buf + amount, size, nmemb - amount, fp);
+	}
 	if ( !fp->read_func ) { errno = EBADF; return 0; }
 	fp->flags &= ~_FILE_LAST_WRITE; fp->flags |= _FILE_LAST_READ;
 	return fp->read_func(ptr, size, nmemb, fp->user);
@@ -96,6 +108,7 @@ size_t fwrite(const void* ptr, size_t size, size_t nmemb, FILE* fp)
 
 int fseeko(FILE* fp, off_t offset, int whence)
 {
+	fp->numpushedback = 0;
 	return (fp->seek_func) ? fp->seek_func(fp->user, offset, whence) : 0;
 }
 
@@ -122,6 +135,7 @@ int ferror(FILE* fp)
 
 int feof(FILE* fp)
 {
+	if ( fp->numpushedback ) { return 0; }
 	if ( !fp->eof_func ) { return 0; }
 	return fp->eof_func(fp->user);
 }
@@ -135,7 +149,7 @@ void rewind(FILE* fp)
 off_t ftello(FILE* fp)
 {
 	if ( !fp->tell_func ) { errno = EBADF; return -1; }
-	return fp->tell_func(fp->user);
+	return fp->tell_func(fp->user) - fp->numpushedback;
 }
 
 long ftell(FILE* fp)
@@ -143,6 +157,14 @@ long ftell(FILE* fp)
 	return (long) ftello(fp);
 }
 
+int ungetc(int c, FILE* fp)
+{
+	if ( fp->numpushedback == _FILE_MAX_PUSHBACK ) { errno = ERANGE; return EOF; }
+	unsigned char uc = c;
+	fp->pushedback[fp->numpushedback++] = uc;
+	return uc;
+}
+
 int fflush(FILE* fp)
 {
 	if ( !fp )
diff --git a/libmaxsi/include/stdio.h b/libmaxsi/include/stdio.h
index 361e6e26..71e18188 100644
--- a/libmaxsi/include/stdio.h
+++ b/libmaxsi/include/stdio.h
@@ -107,6 +107,7 @@ extern char* sortix_gets(void);
 extern int sortix_puts(const char* str);
 extern int sprintf(char* restrict s, const char* restrict format, ...);
 extern int sscanf(const char* restrict s, const char* restrict format, ...);
+extern int ungetc(int c, FILE* stream);
 extern int vfprintf(FILE* restrict stream, const char* restrict format, __gnuc_va_list ap);
 extern int vprintf(const char* restrict format, __gnuc_va_list ap);
 extern int vsnprintf(char* restrict, size_t, const char* restrict, __gnuc_va_list);
@@ -134,7 +135,6 @@ extern int rename(const char* oldname, const char* newname);
 extern int renameat(int oldfd, const char* oldname, int newfd, const char* newname);
 extern int scanf(const char* restrict format, ...);
 extern int setvbuf(FILE* restrict stream, char* restrict buf, int type, size_t size);
-extern int ungetc(int c, FILE* stream);
 extern int vdprintf(int fildes, const char* restrict format, __gnuc_va_list ap);
 extern int vfscanf(FILE* restrict stream, const char* restrict format, __gnuc_va_list arg);
 extern int vscanf(const char* restrict format, __gnuc_va_list arg);