giuseros commented on a change in pull request #6771:
URL: https://github.com/apache/incubator-tvm/pull/6771#discussion_r512580932
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File path: src/arith/const_int_bound.cc
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@@ -259,9 +259,28 @@ class ConstIntBoundAnalyzer::Impl
}
} else {
ICHECK(!b.is_const(0)) << "floormod by zero";
- // mod by negative value is rare,
- // and we just use the simpliest rule.
- return Everything(op->dtype);
+ /* let a / b = x + y, where x is integer, y \in [0, 1)
+ * floormod(a, b) = a - floordiv(a, b) * b
+ * floordiv(a, b) = x
+ * floormod(a, b) = a - floordiv(a, b) * b
+ * = a - x * b
+ * = a - (a / b - y) * b
+ * = a - a + y * b
+ * = y * b
+ * note that 0 <= y < 1
+ * when b > 0, 0 <= b * y < b
+ * 0 <= b * y <= b - 1
+ * when b < 0, b < b * y <= 0
+ * b + 1 <= b * y <= 0
+ * In all cases, min(0, b + 1) <= b * y <= max(0, b - 1)
+ * min(0, b_min + 1) <= b * y <= max(0, b_max - 1)
+ * That is, min(0, b_min + 1) <= floormod(a, b) <= max(0, b_max - 1)
+ */
+ int64_t b_min_cap = InfAwareAdd(b.min_value, 1);
Review comment:
Just a suggestion: why don't you move this (very well done) explanation
at the beginning of the function? It seems to cover more than just the `else`
branch
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