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0344-Handle-negative-zeros-on-unary-minus.patch
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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
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