shithub: nanobsp

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use higher precision for `along` value in BSP_ComputeIntersection().

The previous calculation could produce zero when splitting a long seg
very close to the end, causing a bad split where the new piece was
identical to the old piece, which in turn lead to an infinite loop
which either overflowed the stack or ran out of memory.

--- a/nano_bsp.c

+++ b/nano_bsp.c

@@ -557,17 +557,18 @@

 		}

 	}

-	fixed_t along = FixedDiv (a, a + b);

+	// this is higher precision: 2.30 instead of 16.16

+	fixed_t along = ((int64_t)a << 30) / (int64_t)(a + b);

 	if (seg->v1->x == seg->v2->x)

 		*x = seg->v1->x;

 	else

-		*x = seg->v1->x + FixedMul (seg->v2->x - seg->v1->x, along);

+		*x = seg->v1->x + (((int64_t)(seg->v2->x - seg->v1->x) * (int64_t)along) >> 30);

 	if (seg->v1->y == seg->v2->y)

 		*y = seg->v1->y;

 	else

-		*y = seg->v1->y + FixedMul (seg->v2->y - seg->v1->y, along);

+		*y = seg->v1->y + (((int64_t)(seg->v2->y - seg->v1->y) * (int64_t)along) >> 30);

 }

 //

-- 

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