File 0344-Handle-negative-zeros-on-unary-minus.patch of Package erlang
From 200842d9ae5b75ccc2f982de36742003e231c0bb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Valim?= <jose.valim@dashbit.co>
Date: Thu, 3 Dec 2020 09:39:07 +0100
Subject: [PATCH] Handle negative zeros on unary minus
Before this patch, unary minus "-value" was implemented
as "0 - value" but that is not equivalent for floats when
0.0 is given.
This patch addresses this issue by implementing unary
minus as its own operation and improves the coverage.
---
erts/emulator/beam/emu/arith_instrs.tab | 39 +++++++++++++
erts/emulator/beam/emu/ops.tab | 4 +-
erts/emulator/beam/erl_arith.c | 67 +++++++++++++++++++++-
erts/emulator/beam/global.h | 1 +
erts/emulator/beam/jit/beam_asm.hpp | 2 +
erts/emulator/beam/jit/instr_arith.cpp | 76 +++++++++++++++++++++++++
erts/emulator/beam/jit/ops.tab | 4 +-
erts/emulator/test/float_SUITE.erl | 19 ++++++-
8 files changed, 207 insertions(+), 5 deletions(-)
diff --git a/erts/emulator/beam/erl_arith.c b/erts/emulator/beam/erl_arith.c
index 27a158b27d..fc0ec253fd 100644
--- a/erts/emulator/beam/erl_arith.c
+++ b/erts/emulator/beam/erl_arith.c
@@ -79,7 +79,7 @@ BIF_RETTYPE splus_2(BIF_ALIST_2)
BIF_RETTYPE sminus_1(BIF_ALIST_1)
{
- BIF_RET(erts_mixed_minus(BIF_P, make_small(0), BIF_ARG_1));
+ BIF_RET(erts_unary_minus(BIF_P, BIF_ARG_1));
}
BIF_RETTYPE sminus_2(BIF_ALIST_2)
@@ -461,6 +461,71 @@ erts_mixed_plus(Process* p, Eterm arg1, Eterm arg2)
}
}
+/*
+ * While "-value" is generally the same as "0 - value",
+ * that's not true for floats due to positive and negative
+ * zeros, so we implement unary minus as its own operation.
+ */
+Eterm
+erts_unary_minus(Process* p, Eterm arg)
+{
+ Eterm hdr, res;
+ FloatDef f;
+ dsize_t sz;
+ int need_heap;
+ Eterm* hp;
+ Sint ires;
+
+ ERTS_FP_CHECK_INIT(p);
+ switch (arg & _TAG_PRIMARY_MASK) {
+ case TAG_PRIMARY_IMMED1:
+ switch ((arg & _TAG_IMMED1_MASK) >> _TAG_PRIMARY_SIZE) {
+ case (_TAG_IMMED1_SMALL >> _TAG_PRIMARY_SIZE):
+ ires = -signed_val(arg);
+ if (IS_SSMALL(ires)) {
+ return make_small(ires);
+ } else {
+ hp = HeapFragOnlyAlloc(p, 2);
+ res = small_to_big(ires, hp);
+ return res;
+ }
+ default:
+ badarith:
+ p->freason = BADARITH;
+ return THE_NON_VALUE;
+ }
+ case TAG_PRIMARY_BOXED:
+ hdr = *boxed_val(arg);
+ switch ((hdr & _TAG_HEADER_MASK) >> _TAG_PRIMARY_SIZE) {
+ case (_TAG_HEADER_POS_BIG >> _TAG_PRIMARY_SIZE):
+ case (_TAG_HEADER_NEG_BIG >> _TAG_PRIMARY_SIZE): {
+ Eterm zero_buf[2] = {make_pos_bignum_header(1), 0};
+ Eterm zero = make_big(zero_buf);
+ sz = big_size(arg);
+ need_heap = BIG_NEED_SIZE(sz);
+ hp = HeapFragOnlyAlloc(p, need_heap);
+ res = big_minus(zero, arg, hp);
+ maybe_shrink(p, hp, res, need_heap);
+ ASSERT(is_not_nil(res));
+ return res;
+ }
+ case (_TAG_HEADER_FLOAT >> _TAG_PRIMARY_SIZE):
+ GET_DOUBLE(arg, f);
+ f.fd = -f.fd;
+ ERTS_FP_ERROR(p, f.fd, goto badarith);
+ hp = HeapFragOnlyAlloc(p, FLOAT_SIZE_OBJECT);
+ res = make_float(hp);
+ PUT_DOUBLE(f, hp);
+ return res;
+ default:
+ goto badarith;
+ }
+ default:
+ goto badarith;
+ }
+}
+
+
Eterm
erts_mixed_minus(Process* p, Eterm arg1, Eterm arg2)
{
diff --git a/erts/emulator/beam/global.h b/erts/emulator/beam/global.h
index c8421849d4..f47347d7a5 100644
--- a/erts/emulator/beam/global.h
+++ b/erts/emulator/beam/global.h
@@ -1448,6 +1448,7 @@ Eterm collect_memory(Process *);
void dump_memory_to_fd(int);
int dump_memory_data(const char *);
+Eterm erts_unary_minus(Process* p, Eterm arg1);
Eterm erts_mixed_plus(Process* p, Eterm arg1, Eterm arg2);
Eterm erts_mixed_minus(Process* p, Eterm arg1, Eterm arg2);
Eterm erts_mixed_times(Process* p, Eterm arg1, Eterm arg2);
diff --git a/erts/emulator/test/float_SUITE.erl b/erts/emulator/test/float_SUITE.erl
index 4098aa9c6a..4c450c4398 100644
--- a/erts/emulator/test/float_SUITE.erl
+++ b/erts/emulator/test/float_SUITE.erl
@@ -24,7 +24,7 @@
-export([all/0, suite/0, groups/0,
fpe/1,fp_drv/1,fp_drv_thread/1,denormalized/1,match/1,
- t_mul_add_ops/1,
+ t_mul_add_ops/1,negative_zero/1,
bad_float_unpack/1, write/1, cmp_zero/1, cmp_integer/1, cmp_bignum/1]).
-export([otp_7178/1]).
-export([hidden_inf/1]).
@@ -37,7 +37,7 @@ suite() ->
all() ->
[fpe, fp_drv, fp_drv_thread, otp_7178, denormalized,
match, bad_float_unpack, write, {group, comparison}
- ,hidden_inf
+ ,hidden_inf, negative_zero
,arith, t_mul_add_ops].
groups() ->
@@ -56,6 +56,21 @@ otp_7178(Config) when is_list(Config) ->
{'EXIT', {badarg,_}} = (catch list_to_float("1.0e83291083210")),
ok.
+negative_zero(Config) when is_list(Config) ->
+ <<16#8000000000000000:64>> = do_negative_zero('-', [0.0]),
+ <<16#8000000000000000:64>> = do_negative_zero('*', [-1, 0.0]),
+ <<16#8000000000000000:64>> = do_negative_zero('*', [-1.0, 0.0]),
+ <<16#8000000000000000:64>> = do_negative_zero('*', [-1.0, 0]),
+ ok.
+
+do_negative_zero(Op, Ops) ->
+ Res = <<(my_apply(erlang, Op, Ops))/float>>,
+ Res = <<(case {Op, Ops} of
+ {'-', [A]} -> -A;
+ {'*', [A, B]} -> A * B
+ end)/float>>,
+ Res.
+
%% Forces floating point exceptions and tests that subsequent, legal,
%% operations are calculated correctly. Original version by Sebastian
%% Strollo.
--
2.26.2
