Output NaN payloads only

As discussed with @binji and @sunfish in https://github.com/WebAssembly/sexpr-wasm-prototype/issues/28

2 files changed, 16 insertions, 10 deletions

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)) {
diff --git a/test/llvm_autogenerated/immediates.wast b/test/llvm_autogenerated/immediates.wast
index 85763fe54..19c8c0087 100644
--- a/test/llvm_autogenerated/immediates.wast
+++ b/test/llvm_autogenerated/immediates.wast
@@ -136,7 +136,7 @@
     (block $fake_return_waka123
       (block
         (br $fake_return_waka123
-          (f32.const nan:0x7fc00000)
+          (f32.const nan:0x0)
         )
       )
     )
@@ -145,7 +145,7 @@
     (block $fake_return_waka123
       (block
         (br $fake_return_waka123
-          (f32.const nan:0xffc00000)
+          (f32.const -nan:0x0)
         )
       )
     )
@@ -208,7 +208,7 @@
     (block $fake_return_waka123
       (block
         (br $fake_return_waka123
-          (f64.const nan:0x7ff8000000000000)
+          (f64.const -nan:0x0)
         )
       )
     )
@@ -217,7 +217,7 @@
     (block $fake_return_waka123
       (block
         (br $fake_return_waka123
-          (f64.const nan:0xfff8000000000000)
+          (f64.const nan:0x0)
         )
       )
     )