From 06a575ed69bd45f26283fabae2800278cadf813c Mon Sep 17 00:00:00 2001
From: Paul Kulchenko <paul@kulchenko.com>
Date: Thu, 7 May 2015 22:53:47 -0700
Subject: [PATCH] Added numeric format to preserve floating point precision
 (closes #17).

---
 README.md       |  1 +
 src/serpent.lua |  5 +++--
 t/test.lua      | 12 ++++++++++++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index ec1888a..1de57e9 100644
--- a/README.md
+++ b/README.md
@@ -73,6 +73,7 @@ Similar to `pcall` and `loadstring` calls, `load` returns status as the first va
 * nohuge (true/False) -- disable checking numbers against undefined and huge values
 * maxlevel (number) -- specify max level up to which to expand nested tables
 * maxnum (number) -- specify max number of elements in a table
+* numformat (string; "%.17g") -- specify format for numeric values (shortest possible round-trippable double)
 * valignore (table) -- allows to specify a list of values to ignore (as keys)
 * keyallow (table) -- allows to specify the list of keys to be serialized. Any keys not in this list are not included in final output (as keys)
 * valtypeignore (table) -- allows to specify a list of value *types* to ignore (as keys)
diff --git a/src/serpent.lua b/src/serpent.lua
index 3e7f97e..6961a24 100644
--- a/src/serpent.lua
+++ b/src/serpent.lua
@@ -1,4 +1,4 @@
-local n, v = "serpent", 0.282 -- (C) 2012-15 Paul Kulchenko; MIT License
+local n, v = "serpent", 0.283 -- (C) 2012-15 Paul Kulchenko; MIT License
 local c, d = "Paul Kulchenko", "Lua serializer and pretty printer"
 local snum = {[tostring(1/0)]='1/0 --[[math.huge]]',[tostring(-1/0)]='-1/0 --[[-math.huge]]',[tostring(0/0)]='0/0'}
 local badtype = {thread = true, userdata = true, cdata = true}
@@ -16,11 +16,12 @@ local function s(t, opts)
   local sparse, custom, huge = opts.sparse, opts.custom, not opts.nohuge
   local space, maxl = (opts.compact and '' or ' '), (opts.maxlevel or math.huge)
   local iname, comm = '_'..(name or ''), opts.comment and (tonumber(opts.comment) or math.huge)
+  local numformat = opts.numformat or "%.17g"
   local seen, sref, syms, symn = {}, {'local '..iname..'={}'}, {}, 0
   local function gensym(val) return '_'..(tostring(tostring(val)):gsub("[^%w]",""):gsub("(%d%w+)",
     -- tostring(val) is needed because __tostring may return a non-string value
     function(s) if not syms[s] then symn = symn+1; syms[s] = symn end return tostring(syms[s]) end)) end
-  local function safestr(s) return type(s) == "number" and tostring(huge and snum[tostring(s)] or s)
+  local function safestr(s) return type(s) == "number" and tostring(huge and snum[tostring(s)] or numformat:format(s))
     or type(s) ~= "string" and tostring(s) -- escape NEWLINE/010 and EOF/026
     or ("%q"):format(s):gsub("\010","n"):gsub("\026","\\026") end
   local function comment(s,l) return comm and (l or 0) < comm and ' --[['..select(2, pcall(tostring, s))..']]' or '' end
diff --git a/t/test.lua b/t/test.lua
index ddf28b2..532515e 100644
--- a/t/test.lua
+++ b/t/test.lua
@@ -308,6 +308,18 @@ do
   assert(pcall(serpent.line, a) == true, "`__tostring` method that returns an error is still serialized correctly.")
 end
 
+do
+  local a = serpent.line({ pi = math.pi })
+  local ok, t = serpent.load(a)
+  assert(ok, "pi is serialized and deserialized (1/2): failed")
+  assert(math.pi == t.pi, "pi is deserialized with the same value as the original (1/2): failed")
+
+  a = serpent.line({pi = math.pi}, {numformat = "%1.16e"})
+  ok, t = serpent.load(a)
+  assert(ok, "pi is serialized and deserialized (2/2): failed")
+  assert(math.pi == t.pi, "pi is deserialized with the same value as the original with '%1.16e' format (2/2): failed")
+end
+
 -- based on https://gist.github.com/mpeterv/8360307
 local function random_var(is_key, deep)
   local key = math.random(1000)