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Fix overflow in Counter.add16. #114

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Fix overflow in Counter.add16. #114

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3 changes: 1 addition & 2 deletions src/cipher_block.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -118,8 +118,7 @@ module Counter = struct
let add8 cs i x =
BE.(set_uint64 cs i (Int64.add x (get_uint64 cs i)))

(* FIXME: overflow: higher order bits. *)
let add16 cs i x = add8 cs (i + 8) x
let add16 cs i x = Native.add16be cs.buffer i x

end

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1 change: 1 addition & 0 deletions src/native.ml
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Expand Up @@ -79,5 +79,6 @@ external xor_into : buffer -> off -> buffer -> off -> size -> unit = "caml_nc_xo

external count8be : buffer -> off -> buffer -> off -> size -> unit = "caml_nc_count_8_be" [@@noalloc]
external count16be : buffer -> off -> buffer -> off -> size -> unit = "caml_nc_count_16_be" [@@noalloc]
external add16be : buffer -> off -> int64 -> unit = "caml_nc_add_16_be" [@@noalloc]

external blit : buffer -> off -> buffer -> off -> size -> unit = "caml_blit_bigstring_to_bigstring" [@@noalloc]
16 changes: 16 additions & 0 deletions src/native/misc.c
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Expand Up @@ -48,6 +48,16 @@ static inline void nc_count_16_be (uint64_t *init, uint64_t *dst, size_t blocks)
}
}

static inline void nc_add_16_be (uint64_t *init, uint64_t n) {
uint64_t h = be64_to_cpu (init[0]);
uint64_t l = be64_to_cpu (init[1]);
uint64_t nl = l + n; /* let it wrap */

if (nl < l)
h++;
init[0] = cpu_to_be64 (h);
init[1] = cpu_to_be64 (nl);
}

CAMLprim value
caml_nc_xor_into (value b1, value off1, value b2, value off2, value n) {
Expand All @@ -70,3 +80,9 @@ caml_nc_count_16_be (value init, value off1, value dst, value off2, value blocks
Long_val (blocks) );
return Val_unit;
}

CAMLprim value
caml_nc_add_16_be (value init, value off, value n) {
nc_add_16_be ( (uint64_t *) _ba_uint8_off (init, off), Int64_val(n));
return Val_unit;
}