tests/basics: Add tests for edge cases of nan-box's 47-bit small int.

tests/basics/builtin_abs_intbig.py

@@ -7,3 +7,7 @@ print(abs(-123456789012345678901234567890))
 # edge cases for 32 and 64 bit archs (small int overflow when negating)
 print(abs(-0x3fffffff - 1))
 print(abs(-0x3fffffffffffffff - 1))
+
+# edge case for nan-boxing with 47-bit small int
+i = -0x3fffffffffff
+print(abs(i - 1))

tests/basics/int_big1.py

@@ -90,6 +90,11 @@ x = 1073741823 # small
 x = -1073741823 # small
 x = 1073741824 # big
 x = -1073741824 # big
+# for nan-boxing with 47-bit small ints
+print(int('0x3fffffffffff', 16)) # small
+print(int('-0x3fffffffffff', 16)) # small
+print(int('0x400000000000', 16)) # big
+print(int('-0x400000000000', 16)) # big
 # for 64 bit archs
 x = 4611686018427387903 # small
 x = -4611686018427387903 # small

tests/basics/int_big_add.py

@@ -5,6 +5,11 @@ i = 0x3fffffff
 print(i + i)
 print(-i + -i)
 
+# 47-bit overflow
+i = 0x3fffffffffff
+print(i + i)
+print(-i + -i)
+
 # 63-bit overflow
 i = 0x3fffffffffffffff
 print(i + i)