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adebad07e0
With a dereferenced type-cast pointer as memory operand, gcc 4.6 and later will sometimes copy the data to a temporary location, the address of which is used as the operand value, if it thinks the target address might be misaligned. Using a pointer to a packed struct type instead does the right thing. The 16-bit case is special since the ldrh instruction addressing modes are limited compared to ldr. The "Uq" constraint produces a memory reference suitable for an ldrsb instruction, which supports the same addressing modes as ldrh. However, the restrictions appear to apply only when the operand addresses a single byte. The memory reference must thus be split into two operands each targeting one byte. Finally, the "Uq" constraint is only available in ARM mode. The Thumb-2 ldrh instruction supports most addressing modes so the normal "m" constraint can be used there. Signed-off-by: Mans Rullgard <mans@mansr.com>
85 lines
2.3 KiB
C
85 lines
2.3 KiB
C
/*
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* This file is part of Libav.
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*
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* Libav is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* Libav is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with Libav; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef AVUTIL_ARM_INTREADWRITE_H
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#define AVUTIL_ARM_INTREADWRITE_H
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#include <stdint.h>
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#include "config.h"
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#if HAVE_FAST_UNALIGNED && HAVE_INLINE_ASM
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#define AV_RN16 AV_RN16
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static av_always_inline unsigned AV_RN16(const void *p)
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{
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const uint8_t *q = p;
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unsigned v;
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#ifdef __thumb__
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__asm__ ("ldrh %0, %1" : "=r"(v) : "m"(q[0]), "m"(q[1]));
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#else
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__asm__ ("ldrh %0, %1" : "=r"(v) : "Uq"(q[0]), "m"(q[1]));
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#endif
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return v;
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}
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#define AV_WN16 AV_WN16
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static av_always_inline void AV_WN16(void *p, uint16_t v)
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{
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__asm__ ("strh %1, %0" : "=m"(*(uint16_t *)p) : "r"(v));
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}
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#define AV_RN32 AV_RN32
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static av_always_inline uint32_t AV_RN32(const void *p)
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{
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const struct __attribute__((packed)) { uint32_t v; } *q = p;
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uint32_t v;
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__asm__ ("ldr %0, %1" : "=r"(v) : "m"(*q));
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return v;
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}
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#define AV_WN32 AV_WN32
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static av_always_inline void AV_WN32(void *p, uint32_t v)
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{
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__asm__ ("str %1, %0" : "=m"(*(uint32_t *)p) : "r"(v));
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}
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#define AV_RN64 AV_RN64
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static av_always_inline uint64_t AV_RN64(const void *p)
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{
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const struct __attribute__((packed)) { uint32_t v; } *q = p;
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uint64_t v;
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__asm__ ("ldr %Q0, %1 \n\t"
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"ldr %R0, %2 \n\t"
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: "=&r"(v)
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: "m"(q[0]), "m"(q[1]));
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return v;
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}
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#define AV_WN64 AV_WN64
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static av_always_inline void AV_WN64(void *p, uint64_t v)
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{
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__asm__ ("str %Q2, %0 \n\t"
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"str %R2, %1 \n\t"
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: "=m"(*(uint32_t*)p), "=m"(*((uint32_t*)p+1))
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: "r"(v));
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}
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#endif /* HAVE_INLINE_ASM */
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#endif /* AVUTIL_ARM_INTREADWRITE_H */
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