Add a comment to oltp_common.lua.

Based on #103, add a comment to oltp_common.lua to explain that it
should not be called directly, but is meant to be included by other OLTP
scripts.

sysbench/lua/internal/sysbench.rand.lua

@@ -0,0 +1,75 @@
+-- Copyright (C) 2016-2017 Alexey Kopytov <akopytov@gmail.com>
+
+-- This program is free software; you can redistribute it and/or modify
+-- it under the terms of the GNU General Public License as published by
+-- the Free Software Foundation; either version 2 of the License, or
+-- (at your option) any later version.
+
+-- This program is distributed in the hope that it will be useful,
+-- but WITHOUT ANY WARRANTY; without even the implied warranty of
+-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+-- GNU General Public License for more details.
+
+-- You should have received a copy of the GNU General Public License
+-- along with this program; if not, write to the Free Software
+-- Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+ffi = require("ffi")
+
+-- ----------------------------------------------------------------------
+-- Pseudo-random number generation API
+-- ----------------------------------------------------------------------
+
+sysbench.rand = {}
+
+ffi.cdef[[
+uint64_t sb_rand_uniform_uint64(void);
+uint32_t sb_rand_default(uint32_t, uint32_t);
+uint32_t sb_rand_uniform(uint32_t, uint32_t);
+uint32_t sb_rand_gaussian(uint32_t, uint32_t);
+uint32_t sb_rand_special(uint32_t, uint32_t);
+uint32_t sb_rand_pareto(uint32_t, uint32_t);
+uint32_t sb_rand_unique(void);
+void sb_rand_str(const char *, char *);
+double sb_rand_uniform_double(void);
+]]
+
+function sysbench.rand.uniform_uint64()
+   return ffi.C.sb_rand_uniform_uint64()
+end
+
+function sysbench.rand.default(a, b)
+   return ffi.C.sb_rand_default(a, b)
+end
+
+function sysbench.rand.uniform(a, b)
+   return ffi.C.sb_rand_uniform(a, b)
+end
+
+function sysbench.rand.gaussian(a, b)
+   return ffi.C.sb_rand_gaussian(a, b)
+end
+
+function sysbench.rand.special(a, b)
+   return ffi.C.sb_rand_special(a, b)
+end
+
+function sysbench.rand.pareto(a, b)
+   return ffi.C.sb_rand_pareto(a, b)
+end
+
+function sysbench.rand.unique()
+   return ffi.C.sb_rand_unique()
+end
+
+function sysbench.rand.string(fmt)
+   local buflen = #fmt
+   local buf = ffi.new("uint8_t[?]", buflen)
+   ffi.C.sb_rand_str(fmt, buf)
+   return ffi.string(buf, buflen)
+end
+
+function sysbench.rand.uniform_double()
+   return ffi.C.sb_rand_uniform_double()
+end
+

sysbench/lua/oltp_common.lua

@@ -14,9 +14,10 @@
 -- along with this program; if not, write to the Free Software
 -- Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 
--- ----------------------------------------------------------------------
--- Common code for OLTP benchmarks
--- ----------------------------------------------------------------------
+-- -----------------------------------------------------------------------------
+-- Common code for OLTP benchmarks. This script is meant to be included by other
+-- OLTP script and should not be called directly.
+-- -----------------------------------------------------------------------------
 
 -- Generate strings of random digits with 11-digit groups separated by dashes
 function get_c_value()