• Guillaume Chatelet (38/38) Mar 03 2017 Context:
• Johan Engelen (7/22) Mar 03 2017 Clang without/with optimizations turned on:
• Guillaume Chatelet (4/10) Mar 03 2017 Thx Johan I should have checked... My point is moot then.
• Fool (4/10) Mar 03 2017 GCC with optimizations turned on:

Guillaume Chatelet <chatelet.guillaume gmail.com> writes:

Context: 
http://forum.dlang.org/post/qybweycrifqgtcssepgx forum.dlang.org

---  prints 1 ---
void main(string[] args)
{
     import std.stdio;
     import core.stdc.fenv;
     fesetround(FE_UPWARD);
     writefln("%.32g", 1.0f + float.min_normal);
}
---

--- prints 1.00000011920928955078125 ---
void main(string[] args)
{
     import std.stdio;
     import core.stdc.fenv;
     fesetround(FE_UPWARD);
     float x = 1.0f;
     x += float.min_normal;
     writefln("%.32g", x);
}
---

Considering the floating point operations have a runtime 
component, it seems to me that constant folding is not allowed to 
occur in the first example. For example, it does not occur in the 
following C++ snippet:
---
#include <limits>
#include <cstdio>
#include <cfenv>

int main(int, char**) {
     std::fesetround(FE_UPWARD);
     printf("%.32g\n", std::numeric_limits<float>::denorm_min() + 
1.0f);
     return 0;
}
---

Thoughts?

Johan Engelen <j j.nl> writes:

On Friday, 3 March 2017 at 09:31:19 UTC, Guillaume Chatelet wrote:
 
 Considering the floating point operations have a runtime 
 component, it seems to me that constant folding is not allowed 
 to occur in the first example. For example, it does not occur 
 in the following C++ snippet:
 ---
 #include <limits>
 #include <cstdio>
 #include <cfenv>

 int main(int, char**) {
     std::fesetround(FE_UPWARD);
     printf("%.32g\n", std::numeric_limits<float>::denorm_min() 
 + 1.0f);
     return 0;
 }

Clang without/with optimizations turned on:
❯ clang++ float.cpp && ./a.out
1.00000011920928955078125

❯ clang++ float.cpp -O3 && ./a.out
1

-Johan

Guillaume Chatelet <chatelet.guillaume gmail.com> writes:

On Friday, 3 March 2017 at 22:35:15 UTC, Johan Engelen wrote:
 Clang without/with optimizations turned on:
 ❯ clang++ float.cpp && ./a.out
 1.00000011920928955078125

 ❯ clang++ float.cpp -O3 && ./a.out
 1

 -Johan

Thx Johan I should have checked... My point is moot then.

--
"welcome to the magician world" - Don Clugston | DConf2016

Fool <fool dlang.org> writes:

On Friday, 3 March 2017 at 22:35:15 UTC, Johan Engelen wrote:
 Clang without/with optimizations turned on:
 ❯ clang++ float.cpp && ./a.out
 1.00000011920928955078125

 ❯ clang++ float.cpp -O3 && ./a.out
 1

 -Johan

GCC with optimizations turned on:
$ g++ float.cpp -O3 -frounding-math && ./a.out
1.00000011920928955078125