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a1ec8ff493
Naturally, fixed-width integer arithmetics can overflow. Chibi handles it pretty well in general, but one case was missing: it is negation of the minimal negative number that can be represented as a fixnum. That is, sexp_fx_neg() must not be applied to sexp_make_fixnum(SEXP_MIN_FIXNUM) because it overflows and returns an identical fixnum back. sexp_fx_neg() itself seems to be used right in the current code, but sexp_fx_abs()--which is defined in terms of sexp_fx_neg()--could be applied to the forbidden number when used to retrieve an unboxed value via the sexp_unbox_fixnum(sexp_fx_abs(x)) pattern. So I have added a separate macro that safely calculates unboxed absolute value of a fixnum, and replaced sexp_unbox_fixnum(sexp_fx_abs(x)) usages with it. Current implementation uses two-bit tag for fixnums, plus we need one bit for the sign, so fixnums have (machine word - 3) significant bits. Regression tests cover word sizes of 16, 32, 64, and 128 bits (for the sake of past- and future-proofness). sexp_bignum_expt() does not have a regression test because we need to check it with negative exponents like -2^29, so the base must be over at least 2^(2^29) for the differences to be visible. Fun fact: bignum representation of such number takes around 1/32 of the available user- space memory, which makes testing on anything except 32-bit systems unreasonable (4 TB of RAM anyone?) |
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| .. | ||
| bignum.h | ||
| eval.h | ||
| features.h | ||
| sexp-huff.h | ||
| sexp-hufftabdefs.h | ||
| sexp-hufftabs.c | ||
| sexp-hufftabs.h | ||
| sexp-unhuff.h | ||
| sexp.h | ||