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USE flags

• abi_mips_n32 - 64-bit (32-bit pointer) libraries
• abi_mips_n64 - 64-bit libraries
• abi_mips_o32 - 32-bit libraries
• abi_s390_32 - 32-bit (s390) libraries
• abi_s390_64 - 64-bit (s390x) libraries
• abi_x86_32 - 32-bit (x86) libraries
• abi_x86_64 - 64-bit (amd64) libraries
• abi_x86_x32 - x32 ABI libraries
• cpu_flags_arm_neon - Use the NEON (ASIMD) instruction set
• cpu_flags_ppc_altivec - Use the AltiVec/VMX instruction set
• cpu_flags_x86_avx - Adds support for Advanced Vector Extensions instructions
• cpu_flags_x86_avx2 - Adds support for Advanced Vector Extensions 2 instructions
• cpu_flags_x86_fma3 - Use the Fused Multiply Add 3 instruction set ([fma] in cpuinfo)
• cpu_flags_x86_fma4 - Use the Fused Multiply Add 4 instruction set
• cpu_flags_x86_sse - Use the SSE instruction set
• cpu_flags_x86_sse2 - Use the SSE2 instruction set
• doc - Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally
• fortran - Add support for fortran
• mpi - Add MPI (Message Passing Interface) layer to the apps that support it
• openmp - Build support for the OpenMP (support parallel computing), requires >=sys-devel/gcc-4.2 built with USE="openmp"
• test - Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
• threads - Add threads support for various packages. Usually pthreads
• zbus - Adds support for ZBus cycle-counter of mips