From 7e1d9138b5f088b9ff2e40008c3f2ca9fadcb2ac Mon Sep 17 00:00:00 2001
From: Andrea Mazzoleni <amadvance@gmail.com>
Date: Wed, 28 Oct 2015 19:36:24 +0100
Subject: [PATCH] Add the deplete operation at the data stream

It's used to read the content file up to the end to verify its CRC.
---
 cmdline/state.c  | 21 +------------------
 cmdline/stream.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++--
 cmdline/stream.h | 18 ++++++++++------
 3 files changed, 65 insertions(+), 28 deletions(-)

diff --git a/cmdline/state.c b/cmdline/state.c
index 88295c4e..79344ee7 100644
--- a/cmdline/state.c
+++ b/cmdline/state.c
@@ -1564,26 +1564,7 @@ static void decoding_error(const char* path, STREAM* f)
 
 	log_fatal("Decoding error in '%s' at offset %" PRIi64 "\n", path, stell(f));
 
-	buf[0] = 0;
-	buf[1] = 0;
-	buf[2] = 0;
-	buf[3] = 0;
-
-	/* read until the end of the file */
-	while (1) {
-		int c = sgetc(f);
-		if (c == EOF) {
-			break;
-		}
-
-		/* keep the last four bytes */
-		buf[0] = buf[1];
-		buf[1] = buf[2];
-		buf[2] = buf[3];
-		buf[3] = c;
-	}
-
-	if (serror(f)) {
+	if (sdeplete(f, buf) != 0) {
 		/* LCOV_EXCL_START */
 		log_fatal("Error flushing the content file '%s' at offset %" PRIi64 "\n", path, stell(f));
 		exit(EXIT_FAILURE);
diff --git a/cmdline/stream.c b/cmdline/stream.c
index 82849022..b891e116 100644
--- a/cmdline/stream.c
+++ b/cmdline/stream.c
@@ -174,7 +174,11 @@ int shandle(STREAM* s)
 	return s->handle[0].f;
 }
 
-int sfill(STREAM* s)
+/**
+ * Fill the read stream buffer.
+ * \return 0 if at least on char is read, or EOF on error.
+ */
+static int sfill(STREAM* s)
 {
 	ssize_t ret;
 
@@ -208,7 +212,45 @@ int sfill(STREAM* s)
 	s->pos = s->buffer;
 	s->end = s->buffer + ret;
 
-	return *s->pos++;
+	return 0;
+}
+
+int sdeplete(STREAM* s, unsigned char* last)
+{
+	/* last four bytes */
+	last[0] = 0;
+	last[1] = 0;
+	last[2] = 0;
+	last[3] = 0;
+
+	while (1) {
+		/* increase the position up to 4 bytes before the end */
+		if (s->pos + 4 <= s->end)
+			s->pos = s->end - 4;
+
+		/* insert the last 4 bytes */
+		while (s->pos < s->end) {
+			last[0] = last[1];
+			last[1] = last[2];
+			last[2] = last[3];
+			last[3] = *s->pos++;
+		}
+
+		/* fill again the buffer until the end of the file */
+		if (sfill(s) != 0) {
+			/* on error fail */
+			if (serror(s)) {
+				/* LCOV_EXCL_START */
+				return EOF;
+				/* LCOV_EXCL_STOP */
+			}
+
+			/* on EOF terminate */
+			break;
+		}
+	}
+
+	return 0;
 }
 
 int sflush(STREAM* s)
@@ -267,6 +309,14 @@ uint32_t scrc_stream(STREAM*s)
 	return s->crc_stream ^ CRC_IV;
 }
 
+int sgetc_uncached(STREAM* s)
+{
+	/* if at the end of the buffer, fill it */
+	if (s->pos == s->end && sfill(s) != 0)
+		return EOF;
+	return *s->pos++;
+}
+
 int sgettok(STREAM* f, char* str, int size)
 {
 	char* i = str;
diff --git a/cmdline/stream.h b/cmdline/stream.h
index 885f85ec..ec38d716 100644
--- a/cmdline/stream.h
+++ b/cmdline/stream.h
@@ -129,11 +129,11 @@ int sclose(STREAM* s);
 int shandle(STREAM* s);
 
 /**
- * Fill the read stream buffer and read a char.
- * \note Don't call this directly, but use sgetc().
- * \return The char read, or EOF on error.
+ * Read the stream until the end, and return the latest 4 chars.
+ * The CRC of the file is also computed, and you can get it using scrc().
+ * \return 0 on success, or EOF on error.
  */
-int sfill(STREAM* s);
+int sdeplete(STREAM* s, unsigned char* last);
 
 /**
  * Flush the write stream buffer.
@@ -220,13 +220,19 @@ int ssync(STREAM* s);
 /****************************************************************************/
 /* get */
 
+/**
+ * \internal Used by sgetc().
+ * \note Don't call this directly, but use sgetc().
+ */
+int sgetc_uncached(STREAM* s);
+
 /**
  * Read a char. Like fgetc().
  */
 static inline int sgetc(STREAM* s)
 {
-	if (s->pos == s->end)
-		return sfill(s);
+	if (tommy_unlikely(s->pos == s->end))
+		return sgetc_uncached(s);
 	return *s->pos++;
 }