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Re: [PATCH v3 08/19] qemu/bitops.h: Limit rotate amounts
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From: |
Richard Henderson |
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Subject: |
Re: [PATCH v3 08/19] qemu/bitops.h: Limit rotate amounts |
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Date: |
Tue, 2 May 2023 21:11:16 +0100 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 |
On 4/28/23 15:47, Lawrence Hunter wrote:
static inline uint32_t ror32(uint32_t word, unsigned int shift)
{
- return (word >> shift) | (word << ((32 - shift) & 31));
+ shift &= 31;
+ return (word >> shift) | (word << (32 - shift));
This is incorrect, because if shift == 0, you are now performing (word << 32).
I agree with your original intent though, to mask and accept any rotation.
I've changed these like so:
- return (word >> shift) | (word << ((32 - shift) & 31));
+ return (word >> (shift & 31)) | (word << (-shift & 31));
which also eliminates the useless subtract from word-size-before-mask.
r~