io: refactor string and file work into new unit

kernel/io.h

@@ -0,0 +1,100 @@
+#include "kernel/yosys_common.h"
+#include <string>
+
+#ifndef YOSYS_IO_H
+#define YOSYS_IO_H
+
+#ifdef YOSYS_ENABLE_ZLIB
+#include <zlib.h>
+#endif
+
+YOSYS_NAMESPACE_BEGIN
+
+inline std::string vstringf(const char *fmt, va_list ap)
+{
+	// For the common case of strings shorter than 128, save a heap
+	// allocation by using a stack allocated buffer.
+	const int kBufSize = 128;
+	char buf[kBufSize];
+	buf[0] = '\0';
+	va_list apc;
+	va_copy(apc, ap);
+	int n = vsnprintf(buf, kBufSize, fmt, apc);
+	va_end(apc);
+	if (n < kBufSize)
+		return std::string(buf);
+
+	std::string string;
+	char *str = NULL;
+#if defined(_WIN32) || defined(__CYGWIN__)
+	int sz = 2 * kBufSize, rc;
+	while (1) {
+		va_copy(apc, ap);
+		str = (char *)realloc(str, sz);
+		rc = vsnprintf(str, sz, fmt, apc);
+		va_end(apc);
+		if (rc >= 0 && rc < sz)
+			break;
+		sz *= 2;
+	}
+	if (str != NULL) {
+		string = str;
+		free(str);
+	}
+	return string;
+#else
+	if (vasprintf(&str, fmt, ap) < 0)
+		str = NULL;
+	if (str != NULL) {
+		string = str;
+		free(str);
+	}
+	return string;
+#endif
+}
+
+std::string stringf(const char *fmt, ...) YS_ATTRIBUTE(format(printf, 1, 2));
+
+inline std::string stringf(const char *fmt, ...)
+{
+	std::string string;
+	va_list ap;
+
+	va_start(ap, fmt);
+	string = vstringf(fmt, ap);
+	va_end(ap);
+
+	return string;
+}
+
+#ifdef YOSYS_ENABLE_ZLIB
+/*
+An output stream that uses a stringbuf to buffer data internally,
+using zlib to write gzip-compressed data every time the stream is flushed.
+*/
+class gzip_ostream : public std::ostream {
+public:
+    gzip_ostream();
+    bool open(const std::string &filename);
+private:
+    class gzip_streambuf : public std::stringbuf {
+    public:
+        gzip_streambuf();
+        bool open(const std::string &filename);
+        virtual int sync() override;
+        virtual ~gzip_streambuf();
+    private:
+        static const int buffer_size = 4096;  // Size of the internal buffer
+        char buffer[buffer_size];             // Internal buffer for compressed data
+        gzFile gzf = nullptr;                 // Handle to the gzip file
+    };
+
+    gzip_streambuf outbuf;  // The stream buffer instance
+};
+#endif // YOSYS_ENABLE_ZLIB
+
+std::istream* uncompressed(std::ifstream* f, const std::string filename);
+
+YOSYS_NAMESPACE_END
+
+#endif // YOSYS_IO_H