Xcode / LLDB script for formatting half-precision floats in the debugger.

half.hpp

union FP16
{
    uint16 u;
    struct
    {
        uint16 Mantissa : 10;
        uint16 Exponent : 5;
        uint16 Sign : 1;
    };
};

struct half
{
    // Constructors, operators, etc... here

    FP16 fp16;
};

Half.py

import lldb

# FP16 summary
def summary_FP16( valobj, internal_dict ):
    anon = valobj.GetChildAtIndex(1)
    m = anon.GetChildAtIndex(0).GetValueAsUnsigned()
    e = anon.GetChildAtIndex(1).GetValueAsUnsigned()
    s = anon.GetChildAtIndex(2).GetValueAsUnsigned()
    if e == 0:
        summary = "" if s == 0 else "-"
        summary += str( 2.0**(-14.0) * (m/1024.0) )
    elif e == 31:
        if m == 0:
            summary = "+Inf" if s == 0 else "-Inf"
        else:
            summary = "NaN"
    else:
        summary = str( (-1.0)**s * 2.0**(e-15.0) * (1.0+m/1024.0) )
    return summary

def __lldb_init_module( debugger, dict ):
    debugger.HandleCommand('type summary add FP16 -w Half -F Half.summary_FP16')
    debugger.HandleCommand('type summary add half -w Half --summary-string "${var.fp16}"')

lldbinit

#
# Copy any referenced python scripts to ~/.lldb/
# Copy this file to ~/.lldbinit and set its execute bit
#

# load up python script for half precision float
command script import ~/.lldb/Half.py

# enable summary formats for Half
type category enable Half