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From Salem Derisavi via TVM Discuss <nore...@discuss.tvm.ai>
Subject [TVM Discuss] [Development] Integer constant folding for division and mod
Date Mon, 25 Mar 2019 18:30:37 GMT


@sgrechanik-h @tqchen @yzhliu
My understanding is that TVM uses truncated division/mod, unlike Halide that uses Euclidean
division/mod. Nevertheless, TVM uses `div_imp` (imlementation below) to do constant folding
for division. Seems like this implementation is coming from Halide source code. This seems
like a bug to me unless I'm missing something. If I get confirmation on this bug, I'll open
an issue and send a PR in Github.

```c++
template<typename T>
inline T div_imp(T a, T b) {
    Type t = type_of<T>();
    if (t.is_int()) {
        int64_t q = a / b;
        int64_t r = a - q * b;
        int64_t bs = b >> (t.bits() - 1);
        int64_t rs = r >> (t.bits() - 1);
        return (T) (q - (rs & bs) + (rs & ~bs));
    } else {
        return a / b;
    }
}
```





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[Visit Topic](https://discuss.tvm.ai/t/integer-constant-folding-for-division-and-mod/2008/1)
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Tianqi Chen, UW, Seattle, WA, 98105, United States
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