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--[[
Given two content-idental string s1, s2, test if they end up to be the
same string object. The purpose of this test is to make sure hash function
do not accidently include extraneous bytes before and after the string in
question.
]]
local ffi = require("ffi")
local C = ffi.C
ffi.cdef[[
void free(void*);
char* malloc(size_t);
void *memset(void*, int, size_t);
void *memcpy(void*, void*, size_t);
long time(void*);
void srandom(unsigned);
long random(void);
]]
local function test_equal(len_min, len_max)
-- source string is wrapped by 16-byte-junk both before and after the
-- string
local x = C.random()
local l = len_min + x % (len_max - len_min);
local buf_len = tonumber(l + 16 * 2)
local src_buf = C.malloc(buf_len)
for i = 0, buf_len - 1 do
src_buf[i] = C.random() % 255
end
-- dest string is the clone of the source string, but it is sandwiched
-- by different junk bytes
local dest_buf = C.malloc(buf_len)
C.memset(dest_buf, 0x5a, buf_len)
local ofst = 8 + (C.random() % 8)
C.memcpy(dest_buf + ofst, src_buf + 16, l);
local str1 = ffi.string(src_buf + 16, l)
local str2 = ffi.string(dest_buf + ofst, l)
C.free(src_buf)
C.free(dest_buf)
if str1 ~= str2 then
-- Oops, look like hash function mistakenly include extraneous bytes
-- close to the string
return 1 -- wtf
end
end
--local lens = {1, 4, 16, 128, 1024}
local lens = {128, 1024}
local iter = 1000
for i = 1, #lens - 1 do
for j = 1, iter do
if test_equal(lens[i], lens[i+1]) ~= nil then
os.exit(1)
end
end
end
os.exit(0)
|
