From 388e50c33dde9de4ab0adea2465c7f0a74e37647 Mon Sep 17 00:00:00 2001
From: Alan Gutierrez <alan@prettyrobots.com>
Date: Sun, 26 Apr 2020 02:35:14 -0500
Subject: [PATCH] Two's compliment packed integers.

Closes #425.
---
 test/cycle/packed.t.js              |  4 ++--
 test/generated/packed.parser.all.js |  2 ++
 test/generated/packed.parser.bff.js |  2 ++
 test/generated/packed.parser.inc.js |  2 ++
 test/language/packed.t.js           |  4 ++--
 unpack.js                           | 14 +++++++++++++-
 6 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/test/cycle/packed.t.js b/test/cycle/packed.t.js
index df0bc41b..3af4ea4e 100644
--- a/test/cycle/packed.t.js
+++ b/test/cycle/packed.t.js
@@ -8,11 +8,11 @@ function prove (okay) {
                 header: {
                     literal: 'deaf',
                     one: 1,
-                    two: 3,
+                    two: -3,
                     three: 12
                 }
             }
         },
-        objects: [{ header: { one: 1, two: 5, three: 1 } }]
+        objects: [{ header: { one: 1, two: -4, three: 1 } }]
     })
 }
diff --git a/test/generated/packed.parser.all.js b/test/generated/packed.parser.all.js
index 8e6e8894..80ac262f 100644
--- a/test/generated/packed.parser.all.js
+++ b/test/generated/packed.parser.all.js
@@ -18,6 +18,8 @@ module.exports = function (parsers) {
 
         object.header.one = $_ >>> 15 & 0x1
         object.header.two = $_ >>> 12 & 0x7
+        object.header.two =
+            object.header.two & 0x4 ? (0x7 - object.header.two  + 1) * -1 : object.header.two
         object.header.three = $_ & 0xfff
 
         return object
diff --git a/test/generated/packed.parser.bff.js b/test/generated/packed.parser.bff.js
index b4f49a1d..d3081897 100644
--- a/test/generated/packed.parser.bff.js
+++ b/test/generated/packed.parser.bff.js
@@ -23,6 +23,8 @@ module.exports = function (parsers) {
 
             object.header.one = $_ >>> 15 & 0x1
             object.header.two = $_ >>> 12 & 0x7
+            object.header.two =
+                object.header.two & 0x4 ? (0x7 - object.header.two  + 1) * -1 : object.header.two
             object.header.three = $_ & 0xfff
 
             return { start: $start, object: object, parse: null }
diff --git a/test/generated/packed.parser.inc.js b/test/generated/packed.parser.inc.js
index ff50a860..762a3b60 100644
--- a/test/generated/packed.parser.inc.js
+++ b/test/generated/packed.parser.inc.js
@@ -32,6 +32,8 @@ module.exports = function (parsers) {
 
                 object.header.one = $_ >>> 15 & 0x1
                 object.header.two = $_ >>> 12 & 0x7
+                object.header.two =
+                    object.header.two & 0x4 ? (0x7 - object.header.two  + 1) * -1 : object.header.two
                 object.header.three = $_ & 0xfff
 
 
diff --git a/test/language/packed.t.js b/test/language/packed.t.js
index 46767dff..1941bdc9 100644
--- a/test/language/packed.t.js
+++ b/test/language/packed.t.js
@@ -5,7 +5,7 @@ require('proof')(1, okay => {
             header: {
                 literal: 'deaf',
                 one: 1,
-                two: 3,
+                two: -3,
                 three: 12
             }
         }
@@ -40,7 +40,7 @@ require('proof')(1, okay => {
                 bits: 3,
                 fixed: true,
                 endianness: 'big',
-                compliment: false
+                compliment: true
             }, {
                 name: 'three',
                 dotted: '.three',
diff --git a/unpack.js b/unpack.js
index 680db350..f09df433 100644
--- a/unpack.js
+++ b/unpack.js
@@ -1,4 +1,6 @@
 const fiddle = require('./fiddle/unpack')
+const unsign = require('./fiddle/unsign')
+const $ = require('programmatic')
 
 function unpack (path, field, assignee) {
     let bits = field.bits, offset = 0, bit = 0
@@ -7,8 +9,18 @@ function unpack (path, field, assignee) {
         bit += field.bits
         return field
     })
+    // TODO Faster with an if statement rather than a reassignment (see
+    // generated code) or with a temporary variable.
     return packing.filter(field => field.type == 'integer').map(function (field) {
-        return `${path}${field.dotted} = ${fiddle(bits, field.offset, field.bits, assignee)}`
+        const assign = `${path}${field.dotted} = ${fiddle(bits, field.offset, field.bits, assignee)}`
+        if (field.compliment) {
+            return $(`
+                `, assign, `
+                ${path}${field.dotted} =
+                    `, unsign(path + field.dotted, field.bits), `
+            `)
+        }
+        return assign
     }).join('\n')
 }