java - GetDirectBufferAddress: Address out by 4 -


i attempting pass bytebuffer java native code in android. consistantly getting returned memory address starting @ index 4.

i have tested across various devices , array same size across java , jni when calling getdirectbuffercapacity.

why offset occuring?

java:

inputbuffer = bytebuffer.allocatedirect(inputbuffersize);

jni:

uint8_t* inputbuffer = (uint8_t*) env->getdirectbufferaddress(inputbytebuffer);

the given memory address offset 4 bytes , moving pointer array match (as shown below).

uint8_t* inputbuffer = (uint8_t*) env->getdirectbufferaddress(inputbytebuffer) - 4;

the address returned effective address, based upon alignment of buffer. code (copyright aosp, rights reserved) looks this:

public static bytebuffer allocatedirect(int capacity) {     if (capacity < 0) {         throw new illegalargumentexception("capacity < 0: " + capacity);     }     // ensure alignment 8.     memoryblock memoryblock = memoryblock.allocate(capacity + 7);     long address = memoryblock.tolong();     long alignedaddress = (address + 7) & ~(long)7;     return new directbytebuffer(memoryblock, capacity, (int)(alignedaddress - address), false, null); }

when direct address, effective address, aligned, while actual buffer not aligned.


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