Messages in this thread | | | Subject | Re: [GIT pull] core/urgent for v5.4-rc7 | From | Joe Perches <> | Date | Sun, 10 Nov 2019 17:50:32 -0800 |
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On Sun, 2019-11-10 at 14:35 -0800, Linus Torvalds wrote: > On Sun, Nov 10, 2019 at 2:01 PM Joe Perches <joe@perches.com> wrote: > > trivia: > > > > This idiom '!!(logical test)' is odd and redundant. > > Logical test result is already 0 or 1, no !! is unnecessary. > > You are of course correct. > > I have to say, I personally have always disliked the idiomatic C "!!" > pattern. I don't think it reads well, although that's probably "C > cultural" - once you are used to the pattern, you don't think of it as > anything else. > > Personally, I prefer "x != 0" over "!!x" since it reads much better to > a human, and is equally legible whether you're used to the !! pattern > or not. > > C is not perl, the Obfuscated C contest not-withstanding. > > And since modern C has bool, if you really want to use a cast-to-bool > instead of "x != 0", I think doing exactly that is preferable to "!!". > > So I think both "x != 0" and "(bool)x" are preferable to "!!x", and > would also have made it obvious how odd and redundant the test was in > this case. > > But "!!x" is shorter, of course. And it you learnt C with that pattern > it looks obvious.
The !! logical usage is not particularly common in the kernel. There seems to be only a couple/few dozen.
$ git grep -P '\!\!\s*\([^\)]+[\!=]=.*\);' drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c: info->realtek_eDPToLVDS = !!(lvds->dplvdsrxid == eDP_TO_LVDS_REALTEK_ID); drivers/iio/resolver/ad2s1200.c: gpiod_set_value(st->rdvel, !!(chan->type == IIO_ANGL)); drivers/infiniband/hw/mlx5/mr.c: MLX5_SET(mkc, mkc, en_rinval, !!((type == IB_MW_TYPE_2))); drivers/leds/leds-max77693.c: *state = !!(*state && (led->strobing_sub_led_id == sub_led->fled_id)); drivers/net/ethernet/qlogic/qed/qed_dcbx.c: return !!(mfw_val == DCBX_APP_SF_IEEE_ETHTYPE); drivers/net/ethernet/qlogic/qed/qed_dcbx.c: return !!(mfw_val == type || mfw_val == DCBX_APP_SF_IEEE_TCP_UDP_PORT); drivers/net/ethernet/qlogic/qed/qed_dcbx.c: return !!(ethtype && (proto_id == QED_ETH_TYPE_DEFAULT)); drivers/net/ethernet/qlogic/qed/qed_dcbx.c: return !!(port && (proto_id == QED_TCP_PORT_ISCSI)); drivers/net/ethernet/qlogic/qed/qed_dcbx.c: return !!(ethtype && (proto_id == QED_ETH_TYPE_FCOE)); drivers/net/ethernet/qlogic/qed/qed_dcbx.c: return !!(ethtype && (proto_id == QED_ETH_TYPE_ROCE)); drivers/net/ethernet/qlogic/qed/qed_dcbx.c: return !!(port && (proto_id == QED_UDP_PORT_TYPE_ROCE_V2)); drivers/net/ethernet/qlogic/qed/qed_dcbx.c: ethtype = !!(idtype == DCB_APP_IDTYPE_ETHTYPE); drivers/net/ethernet/qlogic/qed/qed_dcbx.c: ethtype = !!(idtype == DCB_APP_IDTYPE_ETHTYPE); drivers/net/wireless/ath/ath9k/recv.c: is_40 = !!(rxs->bw == RATE_INFO_BW_40); drivers/pci/controller/pcie-iproc.c: return !!(reg_offset == IPROC_PCIE_REG_INVALID); drivers/pci/controller/pcie-iproc.c: return !!(ib_map->type == type); drivers/pci/hotplug/pnv_php.c: added = !!(presence == OPAL_PCI_SLOT_PRESENT); drivers/platform/x86/asus-wmi.c: ctrl_param = !!(bd->props.power == FB_BLANK_UNBLANK); drivers/scsi/hisi_sas/hisi_sas_main.c: bool do_port_check = !!(_sas_port != sas_port); fs/ocfs2/reservations.c: return !!(resv->r_len == 0); fs/ubifs/journal.c: int last_reference = !!(deletion && inode->i_nlink == 0); fs/ubifs/journal.c: int last_reference = !!(new_inode && new_inode->i_nlink == 0); sound/firewire/amdtp-stream.c: !!(params->header_length == 0 && params->payload_length == 0); tools/perf/util/time-utils.c: num += !!(*cp == ',');
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