root/test/warning/float16_t_underflow.cpp

DEFINITIONS

1. h_assert
2. main

#include "Halide.h"
#include <stdio.h>
#include <cmath>

using namespace Halide;

// FIXME: Why aren't we using a unit test framework for this?
void h_assert(bool condition, const char* msg) {
    if (!condition) {
        printf("FAIL: %s\n", msg);
        abort();
    }
}

int main() {
    // Number is subnormal as a float but when converting to
    // half it will not be representable forcing rounding to occur
    const float verySmallNum = (1.0f)/(1<<25);
    
    h_assert(verySmallNum != 0.0, "smallNum should not be 0");
    
    // This should trigger an underflow (IEEE754 7.5 Underflow) warning
    //
    // Basically if the result computed as if we had an unbounded exponent but
    // did the rounding would be
    // - subnormal
    // AND
    // - non zero
    // and the actual result returned (distinct from the result described above)
    // is not exact (i.e. rounding occurred when using the finite exponenet)
    // then underflow should be flagged.
    float16_t warning(verySmallNum, RoundingMode::ToNearestTiesToAway);
    h_assert(warning.to_bits() == 0x0001, "bits incorrect");
    
    // Supress GCC's -Wunused-but-set-variable
    warning.is_infinity();
    return 0;
}