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author | shyouhei <shyouhei@b2dd03c8-39d4-4d8f-98ff-823fe69b080e> | 2018-11-20 04:51:09 +0000 |
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committer | shyouhei <shyouhei@b2dd03c8-39d4-4d8f-98ff-823fe69b080e> | 2018-11-20 04:51:09 +0000 |
commit | 0deee5c0aaf7a1b6a78bf4513fdd3a59475bfcf8 (patch) | |
tree | bc263c4743bd4b74204ea9b76edd6019c8635a8c /vm_insnhelper.c | |
parent | 0dfc5918ec19cb67d8a49915ad8ab177f56e4e73 (diff) |
vm_insnhelper.c: recv -1 + 3 overflows
Here, recv can be INT2FIX(-1), which is 0xFFFF_FFFFul.
INT2FIX(1) is 3ul. So `recv - 1 + INT2FIX(1)` is:
recv 0xFFFF_FFFFul
recv-1 0xFFFF_FFFEul (note: unsigned)
recv-1+INT2FIX(1) 0x0000_0001ul Here is the overflow.
Given recv is a Fixnum, it can never be 0xFFFF_FFFD. 0xFFFF_FFFF is
the only value that can overflow this way, so special-casing this
value should just suffice.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65828 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Diffstat (limited to 'vm_insnhelper.c')
-rw-r--r-- | vm_insnhelper.c | 36 |
1 files changed, 29 insertions, 7 deletions
diff --git a/vm_insnhelper.c b/vm_insnhelper.c index ef4c938fc5..04b085571b 100644 --- a/vm_insnhelper.c +++ b/vm_insnhelper.c @@ -3763,17 +3763,39 @@ vm_opt_empty_p(VALUE recv) } static VALUE +fix_succ(VALUE x) +{ + switch (x) { + case ~0UL: + /* 0xFFFF_FFFF == INT2FIX(-1) + * `-1.succ` is of course 0. */ + return INT2FIX(0); + case RSHIFT(~0UL, 1): + /* 0x7FFF_FFFF == LONG2FIX(0x3FFF_FFFF) + * 0x3FFF_FFFF + 1 == 0x4000_0000, which is a Bignum. */ + return rb_uint2big(1UL << (SIZEOF_LONG * CHAR_BIT - 2)); + default: + /* LONG2FIX(FIX2LONG(x)+FIX2LONG(y)) + * == ((lx*2+1)/2 + (ly*2+1)/2)*2+1 + * == lx*2 + ly*2 + 1 + * == (lx*2+1) + (ly*2+1) - 1 + * == x + y - 1 + * + * Here, if we put y := INT2FIX(1): + * + * == x + INT2FIX(1) - 1 + * == x + 2 . + */ + return x + 2; + } +} + +static VALUE vm_opt_succ(VALUE recv) { if (FIXNUM_P(recv) && BASIC_OP_UNREDEFINED_P(BOP_SUCC, INTEGER_REDEFINED_OP_FLAG)) { - /* fixnum + INT2FIX(1) */ - if (recv == LONG2FIX(FIXNUM_MAX)) { - return LONG2NUM(FIXNUM_MAX + 1); - } - else { - return recv - 1 + INT2FIX(1); - } + return fix_succ(recv); } else if (SPECIAL_CONST_P(recv)) { return Qundef; |