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Build failure on powerpc64

Tom Callaway 
An excellent question. It is important to remember two key facts:

1. With gcc on ppc64, long doubles exist, they can be used, just not safely
as constants (and maybe they still can be used safely under specific
conditions?).
2. I am not an expert in either PowerPC64 or gcc. :)

Looking at connections.c, we have (in order):
  * handling long double as a valid case in a switch statement checking size
  * adding long double as a field in the u union define
  * handling long double as a valid case in a switch statement checking size
  * handling long double as a valid case in a switch statement checking size
  * memcpy from the address of a long double

In format.c, we have (in order):
  * conditionally creating private_nearbyintl for R_nearbyintl
  * defining a static const long double tbl[]
  * use exact scaling factor in long double precision

For most of these, it seems safe to leave them as is for ppc64. I would
have thought that the gcc compiler might have had issue with:

connections.c:
              static long double ld1;
                for (i = 0, j = 0; i < len; i++, j += size) {
                    ld1 = (long double) REAL(object)[i];

format.c:
   static const long double tbl[] =

... but it doesn't. Perhaps the original code at issue:

arithmetic.c:
   static LDOUBLE q_1_eps = 1 / LDBL_EPSILON;

only makes gcc unhappy because of the very large value trying to be stored
in the static long double, which would make it span the "folded double" on
that architecture.

*****

It seems that the options are:

A) Patch the one place where the compiler determines it is not safe to use
a static long double on ppc64.
B) Treat PPC64 as a platform where it is never safe to use a static long
double

FWIW, I did run the test suite after applying my patch and all of the tests
pass on ppc64.

Tom


On Fri, Dec 13, 2019 at 5:44 AM Martin Maechler <maechler at stat.math.ethz.ch>
wrote:

  
  


  


  


  
  

    

  

    
      
    
    
Thread (5 messages)

  

  

    
            
        Martin Maechler
        
        Build failure on powerpc64
      
      Dec 13
    
    
      
            
        Tom Callaway
        
        Build failure on powerpc64
      
      Dec 13
    
    
      
            
        Serguei Sokol
        
        Build failure on powerpc64
      
      Dec 13
    
    
      
            
        Tom Callaway
        
        Build failure on powerpc64
      
      Dec 13
    
    
      
            
        Martin Maechler
        
        Build failure on powerpc64
      
      Dec 17