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Editorial Team
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Asked: 2026-05-23T16:13:50+00:00

I’m using NEON SIMD instruction to write a part of an Android app, targeting

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I’m using NEON SIMD instruction to write a part of an Android app, targeting Cortex A8 processors. According to this reference manual, NEON supports 16-bit and 32-bit floats, that is float16_t and float32_t. When I tried using float16_t and all of its associated vector types, I got an error saying that this type is undeclared. When looking through contents of arm_neon.h, I found that this type is indeed undeclared.

Is there a reason for this? ARM’s Advanced SIMD obviously supports such data types and instructions. Has anyone encountered / resolved this? Is it documented anywhere?

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  1. Editorial Team

    Can you specify an example section in the document you linked where these 16 bit float operations are called out? I see quite a few 16 bit integer operations defined. Are you using ARM’s compiler or gcc? And are you talking about SIMD or NEON?

    “NEON™ technology builds on the concept of SIMD with a dedicated module to provide 128-bit wide vector operations, compared to the 32bit wide SIMD in the ARMv6 architecture.”

    EDIT:

    I tried this with no compiler complaints:

    int myfun ( int a)
{
    __fp16 b;

    b=a+1;

    return(b+1);
}

    using this command line:

    arm-none-linux-gnueabi-gcc -S -mcpu=mpcore -mfp16-format=ieee -mfpu=neon-fp16  simd.c

    Using codesourcery lite 2011.03

    arm-none-linux-gnueabi-gcc --version
arm-none-linux-gnueabi-gcc (Sourcery G++ Lite 2011.03-41) 4.5.2
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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