From 700c910cd1be1dcfd84f3a2bc4252a47999b9341 Mon Sep 17 00:00:00 2001
From: JF Bastien <jfb@chromium.org>
Date: Thu, 28 Jan 2016 09:01:07 -0800
Subject: Output NaN payloads only

As discussed with @binji and @sunfish in https://github.com/WebAssembly/sexpr-wasm-prototype/issues/28
---
 src/wasm.h | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

(limited to 'src')

diff --git a/src/wasm.h b/src/wasm.h
index 91c318034..367af082a 100644
--- a/src/wasm.h
+++ b/src/wasm.h
@@ -193,9 +193,12 @@ struct Literal {
       union {
         float ff;
         uint32_t ll;
-      } u;
-      u.ff = f;
-      o << "nan:0x" << std::hex << u.ll << std::dec;
+      } fu, iu;
+      fu.ff = f;
+      memcpy(&iu, &fu, sizeof(fu));
+      bool sign = std::signbit(f);
+      uint32_t payload = ~0xffc00000u & iu.ll;
+      o << (sign ? "-" : "") << "nan:0x" << std::hex << payload << std::dec;
       return;
     }
     printDouble(o, f);
@@ -210,9 +213,12 @@ struct Literal {
       union {
         double dd;
         uint64_t ll;
-      } u;
-      u.dd = d;
-      o << "nan:0x" << std::hex << u.ll << std::dec;
+      } du, iu;
+      du.dd = d;
+      memcpy(&iu, &du, sizeof(du));
+      bool sign = std::signbit(d);
+      uint32_t payload = ~0xfff8000000000000ull & iu.ll;
+      o << (sign ? "" : "-") << "nan:0x" << std::hex << payload << std::dec;
       return;
     }
     if (!std::isfinite(d)) {
-- 
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