handle systems that do not support denormalized floats #49
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A feature of gcc on Intel platforms is to enable the FTZ and DAZ features available on modern Intel CPUs. Those features convert denormal floating point values to zero to avoid expensive and slow exception handling inside the CPU. Details can be found at https://www.intel.com/content/www/us/en/develop/documentation/cpp-compiler-developer-guide-and-reference/top/compiler-reference/floating-point-operations/set-the-ftz-and-daz-flags.html Some Linux distributions now started to make this flag the compiler default and build the standard runtime libraries with this switch turned on. On those systems the definition of least-*-*-float evaluates to zero, no longer adhering to their specification, and as such failing test cases relying on them. Compiling sbcl with this compiler feature explicitly turned off is not preventing this problem from happening since we use functions from libm that is built with this switch turned on and as such will apply the conversions nevertheless to our surprise. Therefore this introduces a new feature "normalize-float" for systems with that behavior. This automatically gets switched on by an automated test. The test is designed to detect similar behavior also on non-Intel systems. The definitions of least-*-*-float are adapted accordingly.
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A feature of gcc on Intel platforms is to enable the FTZ and DAZ features available on modern Intel CPUs. Those features convert denormal floating point values to zero to avoid expensive and slow exception handling inside the CPU. Details can be found at https://www.intel.com/content/www/us/en/develop/documentation/cpp-compiler-developer-guide-and-reference/top/compiler-reference/floating-point-operations/set-the-ftz-and-daz-flags.html
Some Linux distributions now started to make this flag the compiler default and build the standard runtime libraries with this switch turned on. On those systems the definition of least---float evaluates to zero, no longer adhering to their specification, and as such failing test cases relying on them. Compiling sbcl with this compiler feature explicitly turned off is not preventing this problem from happening since we use functions from libm that is built with this switch turned on and as such will apply the conversions nevertheless to our surprise.
Therefore this introduces a new feature "normalize-float" for systems with that behavior. This automatically gets switched on by an automated test. The test is designed to detect similar behavior also on non-Intel systems. The definitions of least---float are adapted accordingly.
This can be found at https://bugs.launchpad.net/sbcl/+bug/2002810 as well.