this change hopefully makes the shm trick work on amd64

src/ringbuffer.c

@@ -30,7 +30,6 @@ ctor(void * _this, va_list * params)
 	long        psize    = sysconf(_SC_PAGESIZE);
 	size_t      size;
 	int         shm;
-	void *      shm_addr;
 
 	this->shm_name = malloc(strlen(shm_name) + 1);
 	strcpy(this->shm_name, shm_name);
@@ -52,25 +51,24 @@ ctor(void * _this, va_list * params)
 			ftruncate(shm, this->bsize);
 		}
 
-		shm_addr = mmap (0, this->bsize<<1,
-				PROT_READ|PROT_WRITE, MAP_SHARED, shm, 0);
-		if (shm_addr == MAP_FAILED)
-			break;
-
-		munmap(shm_addr, this->bsize<<1);
-
-		this->buffer = mmap (shm_addr, this->bsize,
+		this->buffer = mmap (0, this->bsize<<1,
 				PROT_READ|PROT_WRITE, MAP_SHARED, shm, 0);
 		if (this->buffer == MAP_FAILED) {
-			shm_addr = NULL;
+			this->buffer = NULL;
 			break;
 		}   
 
-		this->mirror = mmap (shm_addr + this->bsize, this->bsize,
+		this->mirror = mmap (this->buffer + this->bsize, this->bsize,
 				PROT_READ|PROT_WRITE, MAP_SHARED, shm, 0);
-		if (this->mirror != shm_addr + this->bsize) {
-			shm_addr = NULL;
-			break;
+		if (this->mirror != this->buffer + this->bsize) {
+			if (this->mirror == this->buffer - this->bsize) {
+				this->buffer  = this->mirror;
+				this->mirror += this->bsize;
+			}
+			else {
+				this->mirror = NULL;
+				break;
+			}
 		}   
 
 		state = 1;
@@ -82,10 +80,6 @@ ctor(void * _this, va_list * params)
 	}
 
 	if (1 != state) {
-		if (shm_addr) {
-			munmap(shm_addr, this->bsize<<1);
-		}
-
 		dtor(this);
 	}
 }
@@ -100,12 +94,12 @@ dtor(void * _this)
 		free(this->shm_name);
 	}
 
-	if (this->buffer) {
+	if (NULL != this->buffer) {
 		munmap(this->buffer, this->bsize);
 		this->buffer = NULL;
 	}
 
-	if (this->mirror) {
+	if (NULL != this->mirror) {
 		munmap(this->mirror, this->bsize);
 		this->mirror = NULL;
 	}