Fix compilation when compiler do not support __builtin_clz* #12573

1. 
   532479301 commented at 9:23 am on March 1, 2018: contributor

   #ifdef is not correct since defination is defined to 0 or 1. Should change to #if
2. Consensus: Fix bug when compiler do not support __builtin_clz*

   #ifdef is not correct since defination is defined to 0 or 1. Should change to #if

   18307849b4
3. 
   laanwj commented at 9:32 am on March 1, 2018: member

   This change seems to be correct. These macros are defined like this in src/config/bitcoin-config.h:

   0/* Define to 1 if you have the declaration of `__builtin_clzl', and to 0 if
   1   you don't. */
   2#define HAVE_DECL___BUILTIN_CLZL 0
   

   I’m curious why some defines in that file use #undef/#define and others #define XXX 0 versus #define XXX 1, but this is certainly the latter. That seems to be the cause of the confusion here (are there others?). Adding @theuni as reviewer.

4. laanwj requested review from theuni on Mar 1, 2018
5. laanwj added the label Build system on Mar 1, 2018
6. laanwj renamed this:
   Consensus: Fix bug when compiler do not support __builtin_clz*
   Fix compilation when compiler do not support __builtin_clz*
   on Mar 1, 2018
7. theuni approved
8. 
   theuni commented at 4:25 pm on March 5, 2018: member

   @laanwj Huh, yep, that’s really annoying. The docs even point out that the behavior is wonky: https://www.gnu.org/software/autoconf/manual/autoconf-2.62/html_node/Generic-Declarations.html

   I confirmed that we manage to get the others right, though to be 100% safe in the non-autoconf case (msvc builds that don’t use a config.h, for example) we would need to use a construct like #if defined(foo) && foo.

   utACK 18307849b405f9e2067eaa8091b105838f413707

9. 
   fanquake commented at 5:37 pm on March 5, 2018: member

   utACK 1830784
10. 
    laanwj commented at 5:38 pm on March 5, 2018: member

    we would need to use a construct like #if defined(foo) && foo.

    I think using #if X is better in that case. At least it will fail when X is not defined, which aids in discoverability of the option.

11. laanwj merged this on Mar 5, 2018
12. laanwj closed this on Mar 5, 2018

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532479301 laanwj theuni fanquake

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