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libcg / bfp

Beyond Floating Point - Posit C/C++ implementation
MIT License
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Max posit width #20

Closed Tongdongq closed 5 years ago

Tongdongq commented 5 years ago

What is the maximum posit width? I tested successfully with 32 bits (es=2), but for 33 bits, it doesn't work. I see POSIT_WIDTH = 32 in posit_types.h. And Posit::mBits is of type POSIT_UTYPE, which is uint32_t. I tried small changes in posit_types.h, but that doesn't fix it. Do you know if I can change to 32+ bits easily?

libcg commented 5 years ago

You can try this:

#define POSIT_LUTYPE    uint128_t
#define POSIT_UTYPE     uint64_t
#define POSIT_STYPE     int64_t
#define POSIT_WIDTH     64
#define POSIT_ZERO      ((POSIT_UTYPE)0x0000000000000000LL)
#define POSIT_ONE       ((POSIT_UTYPE)0x4000000000000000LL)
#define POSIT_MONE      ((POSIT_UTYPE)0xC000000000000000LL)
#define POSIT_INF       ((POSIT_UTYPE)0x8000000000000000LL)
#define POSIT_MSB       ((POSIT_UTYPE)0x8000000000000000LL)
#define POSIT_MASK ((POSIT_UTYPE)0xFFFFFFFFFFFFFFFF)
libcg commented 5 years ago

I looked a bit more into it and there's a bunch of places where the code assumes 32-bit. Recent updates will cause compilation to fail if you try to use POSIT_WIDTH > 32. It will certainly be worth revisiting later.