e3d28de8a6
When reading hexadecimal floats, cosmopolitan would previously sometimes
print a number of warnings relating to undefined behavior on left shift:
third_party/gdtoa/gethex.c:172: ubsan warning: signed left shift changed
sign bit or overflowed 12 'int' 28 'int' is undefined behavior
This is because gdtoa assumes left shifts are safe when overflow happens
even on signed integers - this is false: the C standard considers it UB.
This is easy to fix, by simply casting the shifted value to unsigned, as
doing so does not change the value or the semantics of the left shifting
(except for avoiding the undefined behavior, as the C standard specifies
that unsigned overflow yields wraparound, avoiding undefined behaviour).
This commit does this, and adds a testcase that previously triggered UB.
(this also adds test macros to test for exact float equality, instead of
the existing {EXPECT,ASSERT}_FLOAT_EQ macros which only tests inputs for
being "almost equal" (with a significant epsilon) whereas exact equality
makes more sense for certain things such as reading floats from strings,
and modifies other testcases for sscanf/fscanf of floats to utilize it).
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| .. | ||
| calls | ||
| crt | ||
| dlopen | ||
| elf | ||
| fmt | ||
| integral | ||
| intrin | ||
| irq | ||
| isystem | ||
| log | ||
| mem | ||
| nexgen32e | ||
| nt | ||
| proc | ||
| runtime | ||
| sock | ||
| stdio | ||
| str | ||
| sysv | ||
| testlib | ||
| thread | ||
| tinymath | ||
| vga | ||
| x | ||
| ar.h | ||
| assert.h | ||
| atomic.h | ||
| BUILD.mk | ||
| complex.h | ||
| cosmo.h | ||
| ctype.h | ||
| cxxabi.h | ||
| dce.h | ||
| dos.h | ||
| empty.s | ||
| errno.h | ||
| imag.h | ||
| inttypes.h | ||
| iso646.h | ||
| limits.h | ||
| literal.h | ||
| mach.h | ||
| macho.h | ||
| macros.h | ||
| math.h | ||
| paths.h | ||
| README.md | ||
| serialize.h | ||
| stdalign.h | ||
| stdbool.h | ||
| stdckdint.h | ||
| stdlib.h | ||
| temp.h | ||
| testlib-test.txt | ||
| time.h | ||
| unistd.h | ||
| utime.h | ||
| wctype.h | ||
| zip.h | ||
Cosmopolitan Standard Library
This directory defines static archives defining functions, like
printf(), mmap(), win32, etc. Please note that the Cosmopolitan
build configuration doesn't link any C/C++ library dependencies
by default, so you still have the flexibility to choose the one
provided by your system. If you'd prefer Cosmopolitan, just add
$(LIBC) and $(CRT) to your linker arguments.
Your library is compromised of many bite-sized static archives. We use the checkdeps tool to guarantee that the contents of the archives are organized in a logical way that's easy to use with or without our makefile infrastructure, since there's no cyclic dependencies.
The Cosmopolitan Library exports only the most stable canonical
system calls for all supported operating systems, regardless of
which platform is used for compilation. We polyfill many of the
APIs, e.g. read(), write() so they work consistently everywhere
while other apis, e.g. CreateWindowEx(), might only work on one
platform, in which case they become no-op functions on others.
Cosmopolitan polyfill wrappers will usually use the dollar sign naming convention, so they may be bypassed when necessary. This same convention is used when multiple implementations of string library and other performance-critical function are provided to allow Cosmopolitan to go fast on both old and newer computers.
We take an approach to configuration that relies heavily on the
compiler's dead code elimination pass (libc/dce.h). Most of the
code is written so that, for example, folks not wanting support
for OpenBSD can flip a bit in SUPPORT_VECTOR and that code will
be omitted from the build. The same is true for builds that are
tuned using -march=native which effectively asks the library to
not include runtime support hooks for x86 processors older than
what you use.
Please note that, unlike Cygwin or MinGW, Cosmopolitan does not achieve broad support by bolting on a POSIX emulation layer. We do nothing more than (in most cases) stateless API translations that get you 90% of the way there in a fast lightweight manner. We therefore can't address some of the subtle differences, such as the nuances of absolute paths on Windows. Our approach could be compared to something more along the lines of, "the Russians just used a pencil to write in space", versus spending millions researching a pen like NASA.