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authorBjörn Gustavsson <[email protected]>2018-12-13 10:22:36 +0100
committerGitHub <[email protected]>2018-12-13 10:22:36 +0100
commit2bf2b7009905a880f514621e8912508055df437e (patch)
treea8af26e339a45dbd5d6658d46c119078175c9ae6 /erts
parent3825199794da28d79b21052a2e69e2335921d55e (diff)
parentc5bb52143bd28c8ce34e427dbf7f024b6e6a65e1 (diff)
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Merge pull request #2051 from bjorng/bjorn/erts/bignum/OTP-15484
Fix reading beyond end of bignum in integer squaring
Diffstat (limited to 'erts')
-rw-r--r--erts/emulator/beam/big.c12
-rw-r--r--erts/emulator/test/big_SUITE.erl18
2 files changed, 22 insertions, 8 deletions
diff --git a/erts/emulator/beam/big.c b/erts/emulator/beam/big.c
index 84338769e0..dac9574fa5 100644
--- a/erts/emulator/beam/big.c
+++ b/erts/emulator/beam/big.c
@@ -668,27 +668,25 @@ static dsize_t I_mul(ErtsDigit* x, dsize_t xl, ErtsDigit* y, dsize_t yl, ErtsDig
static dsize_t I_sqr(ErtsDigit* x, dsize_t xl, ErtsDigit* r)
{
- ErtsDigit d_next = *x;
ErtsDigit d;
ErtsDigit* r0 = r;
ErtsDigit* s = r;
if ((r + xl) == x) /* "Inline" operation */
*x = 0;
- x++;
while(xl--) {
- ErtsDigit* y = x;
+ ErtsDigit* y;
ErtsDigit y_0 = 0, y_1 = 0, y_2 = 0, y_3 = 0;
ErtsDigit b0, b1;
ErtsDigit z0, z1, z2;
ErtsDigit t;
dsize_t y_l = xl;
-
+
+ d = *x;
+ x++;
+ y = x;
s = r;
- d = d_next;
- d_next = *x;
- x++;
DMUL(d, d, b1, b0);
DSUMc(*s, b0, y_3, t);
diff --git a/erts/emulator/test/big_SUITE.erl b/erts/emulator/test/big_SUITE.erl
index 0a42b09903..5b602dd4dc 100644
--- a/erts/emulator/test/big_SUITE.erl
+++ b/erts/emulator/test/big_SUITE.erl
@@ -168,7 +168,11 @@ eval({op,_,Op,A0,B0}, LFH) ->
Res = eval_op(Op, A, B),
erlang:garbage_collect(),
Res;
-eval({integer,_,I}, _) -> I;
+eval({integer,_,I}, _) ->
+ %% "Parasitic" ("symbiotic"?) test of squaring all numbers
+ %% found in the test data.
+ test_squaring(I),
+ I;
eval({call,_,{atom,_,Local},Args0}, LFH) ->
Args = eval_list(Args0, LFH),
LFH(Local, Args).
@@ -192,6 +196,18 @@ eval_op('bxor', A, B) -> A bxor B;
eval_op('bsl', A, B) -> A bsl B;
eval_op('bsr', A, B) -> A bsr B.
+test_squaring(I) ->
+ %% Multiplying an integer by itself is specially optimized, so we
+ %% should take special care to test squaring. The optimization
+ %% will kick in when the two operands have the same address.
+ Sqr = I * I,
+
+ %% This expression will be multiplied in the usual way, because
+ %% the the two operands for '*' are stored at different addresses.
+ Sqr = I * ((I + id(1)) - id(1)),
+
+ ok.
+
%% Built in test functions
fac(0) -> 1;