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To: Thomas Monjalon <thomas@monjalon.net>
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From: Andy Green <andy@warmcat.com>
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Date: Mon, 14 May 2018 08:05:49 +0800
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Subject: Re: [dpdk-dev] [PATCH v3 18/24] rte_ether.h: explicit cast avoiding
truncation warning
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On 05/14/2018 01:02 AM, Thomas Monjalon wrote:
> 12/05/2018 04:00, Andy Green:
>> /projects/lagopus/src/dpdk/build/include/rte_ether.h:213:13:
>> warning: conversion from 'int' to 'uint8_t'
>> {aka 'unsigned char'} may change value [-Wconversion]
>> addr[0] &= ~ETHER_GROUP_ADDR;
>> /* clear multicast bit */
> [..]
>> rte_memcpy(addr, p, ETHER_ADDR_LEN);
>> - addr[0] &= ~ETHER_GROUP_ADDR; /* clear multicast bit */
>> + addr[0] &= (uint8_t)~ETHER_GROUP_ADDR; /* clear multicast bit */
>> addr[0] |= ETHER_LOCAL_ADMIN_ADDR; /* set local assignment bit */
>
> ETHER_GROUP_ADDR and ETHER_LOCAL_ADMIN_ADDR are defined macros,
> they have no type, so I don't understand the need for casting.
> And I don't understand why it is not needed for ETHER_LOCAL_ADMIN_ADDR.
Both of those manifest constants are 0x1.
But ~ETHER_GROUP_ADDR is a "big number" in an int.
The compiler notices a definite truncation if you try to put 0xfffffffe
in a uint8_t and complains.
If you try to put 0x01 in a uint8_t, the compiler feels it was OK.
-Andy