FLT_MAX equivalent for half floats

I am using the __half type from cuda_fp16.h but have not been able to determine what the FLT_MAX is for this data type.

What is its value?

Is there a macro for this value?

From cuda_fp16.h header file:

16 bits are being used in total: 1 sign bit, 5 bits for the exponent, and the significand is being stored in 10 bits. The total precision is 11 bits. There are 15361 representable numbers within the interval [0.0, 1.0], endpoints included. On average we have log10(2**11) ~ 3.311 decimal digits.

So basically this is IEEE 754-2008 compliant implementation of half-precision floating-point numbers. As far as I know DirectX is using the same format (see d3dx9math.h and d3dx10math.h from DirectX SDK), I am reproducing their definitions here, what you wanted seems to be D3DX_16F_MAX and D3DX_16F_MIN:

#define D3DX_16F_DIG          3                // # of decimal digits of precision
#define D3DX_16F_EPSILON      4.8875809e-4f    // smallest such that 1.0 + epsilon != 1.0
#define D3DX_16F_MANT_DIG     11               // # of bits in mantissa
#define D3DX_16F_MAX          6.550400e+004    // max value
#define D3DX_16F_MAX_10_EXP   4                // max decimal exponent
#define D3DX_16F_MAX_EXP      15               // max binary exponent
#define D3DX_16F_MIN          6.1035156e-5f    // min positive value
#define D3DX_16F_MIN_10_EXP   (-4)             // min decimal exponent
#define D3DX_16F_MIN_EXP      (-14)            // min binary exponent
#define D3DX_16F_RADIX        2                // exponent radix
#define D3DX_16F_ROUNDS       1                // addition rounding: near
#define D3DX_16F_SIGN_MASK    0x8000
#define D3DX_16F_EXP_MASK     0x7C00
#define D3DX_16F_FRAC_MASK    0x03FF

Bear in mind however, that this format has other value limitations as described here, not just min/max value limits.