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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>
Libav README ------------ 1) Documentation ---------------- * Read the documentation in the doc/ directory. 2) Licensing ------------ * See the LICENSE file.