From 3ddbfeafde93d1aab16a710498d86eef4e787406 Mon Sep 17 00:00:00 2001
From: Michael Krelin <hacker@klever.net>
Date: Wed, 30 Mar 2005 15:50:28 +0000
Subject: 1. preprocessor doesn't touch unchanged files anymore

2. doublechedk on whether file is up to date when making
3. changed the way preprocessor targets depend on the timestamp file
4. a bugfix in strip_suffix/strip_prefix
---
(limited to 'lib/sitecing_enflesher.ll')

diff --git a/lib/sitecing_enflesher.ll b/lib/sitecing_enflesher.ll
index 5f631d7..46489c7 100644
--- a/lib/sitecing_enflesher.ll
+++ b/lib/sitecing_enflesher.ll
@@ -22,12 +22,7 @@ ID	[A-Za-z_][A-Za-z0-9_]*
     string line = yytext;
     line.erase(0,3);
     line.erase(line.length()-1);
-    outs.flush();
-    outs.close();
-    outs.clear();
-    outs.open((parser.output_basename+line).c_str(),ios::trunc);
-    if(!outs.good())
-	throw preprocessor_error(CODEPOINT,"failed to write preprocessor output");
+    outs_open(parser.output_basename+line);
     anchor();
     anchoraged = true;
 }
@@ -35,12 +30,7 @@ ID	[A-Za-z_][A-Za-z0-9_]*
     string line = yytext;
     line.erase(0,2);
     line.erase(line.length()-1);
-    outs.flush();
-    outs.close();
-    outs.clear();
-    outs.open((parser.output_basename+line).c_str(),ios::trunc);
-    if(!outs.good())
-	throw preprocessor_error(CODEPOINT,"failed to write preprocessor output");
+    outs_open(parser.output_basename+line);
     anchoraged = false;
 }
 
@@ -197,6 +187,68 @@ void sitecing_enflesher::anchor() {
     outs << "\n#line " << lineno() << " \"" << parser.skeleton << "\"\n";
     anchor_time = false;
 }
+
+void sitecing_enflesher::outs_open(const string& nfile) {
+    if(!outs_filename.empty()) {
+	outs.flush();
+	outs.close();
+	outs.clear();
+	/*
+	 * compare source and destination files.
+	 *
+	 * one can also keep a hash for the old one and compute one for the
+	 * output while writing, but I'm not sure if it's any better. Surely a
+	 * bit less accurate, unless we're going to compare it in case of
+	 * difference, anyway.
+	 */
+	bool overwrite = false;
+	struct stat st_s, st_d;
+	string fn_s = outs_filename+".new";
+	string fn_d = outs_filename;
+	if(stat(fn_d.c_str(),&st_d)) {
+	    overwrite = true;
+	}else{
+	    if(stat(fn_s.c_str(),&st_s))
+		throw preprocessor_error(CODEPOINT,"failed to stat() supposedly created file");
+	    if(st_s.st_size!=st_d.st_size) {
+		overwrite = true;
+	    }else{
+		ifstream i_s(fn_s.c_str(),ios::in);
+		if(!i_s)
+		    throw preprocessor_error(CODEPOINT,"failed to open supposedly created file");
+		ifstream i_d(fn_d.c_str(),ios::in);
+		if(!i_d)
+		    throw preprocessor_error(CODEPOINT,"failed to open the old preprocessed source");
+		off_t remaining = st_s.st_size;
+		char t1[2048];
+		char t2[sizeof(t1)];
+		while(remaining) {
+		    int rb = remaining;
+		    if(rb>sizeof(t1))
+			rb = sizeof(t1);
+		    if(i_s.read(t1,rb).gcount()!=rb)
+			throw preprocessor_error(CODEPOINT,"error reading just created file");
+		    if(i_d.read(t2,rb).gcount()!=rb)
+			throw preprocessor_error(CODEPOINT,"error reading the old preprocessed source");
+		    if(memcmp(t1,t2,rb)) {
+			overwrite = true;
+			break;
+		    }
+		    remaining -= rb;
+		}
+	    }
+	}
+	if(overwrite) {
+	    cerr << "renaming '" << fn_s << "'" << endl;
+	    if(rename(fn_s.c_str(),fn_d.c_str()))
+		throw preprocessor_error(CODEPOINT,"failed to rename() generated output");
+	}
+    }
+    outs_filename = nfile;
+    outs.open((nfile+".new").c_str(),ios::trunc);
+    if(!outs.good())
+	throw preprocessor_error(CODEPOINT,"failed to write preprocessor output");
+}
 /*
  * vim:set ft=lex:
  */
--
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