[cairo-commit] src/cairo-fixed-private.h

[Behdad Esfahbod]

 src/cairo-fixed-private.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

New commits:
commit 7f6b57a2386c051e4bb6a156cf14904fe061f837
Author: Behdad Esfahbod <behdad at behdad.org>
Date:   Mon Sep 11 22:00:00 2017 -0700

    Fix undefined-behavior with integer math
    
    As reported to me:
    
    "A calculation on signed integers has undefined behaviour if the result is not
    representable in the type. In this case, it's trying to negate int_min, aka
    -2^31 but the range of an int is [-2^31, 2^31-1] so it doesn't fit. Instead,
    cast to unsigned which has 2's complement wrap-around arithmetic which is what
    this particular function expects."

diff --git a/src/cairo-fixed-private.h b/src/cairo-fixed-private.h
index 9ff8f750..5f9ce684 100644
--- a/src/cairo-fixed-private.h
+++ b/src/cairo-fixed-private.h
@@ -223,7 +223,7 @@ _cairo_fixed_integer_ceil (cairo_fixed_t f)
     if (f > 0)
 	return ((f - 1)>>CAIRO_FIXED_FRAC_BITS) + 1;
     else
-	return - (-f >> CAIRO_FIXED_FRAC_BITS);
+	return - ((cairo_fixed_t)(-(cairo_fixed_unsigned_t)f) >> CAIRO_FIXED_FRAC_BITS);
 }
 
 /* A bunch of explicit 16.16 operators; we need these