lib/ext/qcbor/test/float_tests.c

/*==============================================================================
 float_tests.c -- tests for float and conversion to/from half-precision

 Copyright (c) 2018-2020, Laurence Lundblade. All rights reserved.

 SPDX-License-Identifier: BSD-3-Clause

 See BSD-3-Clause license in README.md

 Created on 9/19/18
 =============================================================================*/

#include "float_tests.h"
#include "qcbor.h"
#include "half_to_double_from_rfc7049.h"
#include <math.h> // For INFINITY and NAN and isnan()



static const uint8_t spExpectedHalf[] = {
    0xB1,
        0x64,
            0x7A, 0x65, 0x72, 0x6F,
        0xF9, 0x00, 0x00,   // 0.000
        0x6A,
            0x69, 0x6E, 0x66, 0x69, 0x6E, 0x69, 0x74, 0x69, 0x74, 0x79,
        0xF9, 0x7C, 0x00,   // Infinity
        0x73,
            0x6E, 0x65, 0x67, 0x61, 0x74, 0x69, 0x76, 0x65, 0x20, 0x69, 0x6E,
            0x66, 0x69, 0x6E, 0x69, 0x74, 0x69, 0x74, 0x79,
        0xF9, 0xFC, 0x00,   // -Inifinity
        0x63,
            0x4E, 0x61, 0x4E,
        0xF9, 0x7E, 0x00,   // NaN
        0x63,
            0x6F, 0x6E, 0x65,
        0xF9, 0x3C, 0x00,   // 1.0
        0x69,
            0x6F, 0x6E, 0x65, 0x20, 0x74, 0x68, 0x69, 0x72, 0x64,
        0xF9, 0x35, 0x55,   // 0.333251953125
        0x76,
            0x6C, 0x61, 0x72, 0x67, 0x65, 0x73, 0x74, 0x20, 0x68, 0x61, 0x6C,
            0x66, 0x2D, 0x70, 0x72, 0x65, 0x63, 0x69, 0x73, 0x69, 0x6F, 0x6E,
        0xF9, 0x7B, 0xFF,   // 65504.0
        0x78, 0x18,
            0x74, 0x6F, 0x6F, 0x2D, 0x6C, 0x61, 0x72, 0x67, 0x65, 0x20, 0x68,
            0x61, 0x6C, 0x66, 0x2D, 0x70, 0x72, 0x65, 0x63, 0x69, 0x73, 0x69,
            0x6F, 0x6E,
        0xF9, 0x7C, 0x00,   // Infinity
        0x72,
            0x73, 0x6D, 0x61, 0x6C, 0x6C, 0x65, 0x73, 0x74, 0x20, 0x73, 0x75,
            0x62, 0x6E, 0x6F, 0x72, 0x6D, 0x61, 0x6C,
        0xF9, 0x00, 0x01,   // 0.000000059604
        0x6F,
            0x73, 0x6D, 0x61, 0x6C, 0x6C, 0x65, 0x73, 0x74, 0x20, 0x6E, 0x6F,
            0x72, 0x6D, 0x61, 0x6C,
        0xF9, 0x03, 0xFF,   // 0.0000609755516
        0x71,
            0x62, 0x69, 0x67, 0x67, 0x65, 0x73, 0x74, 0x20, 0x73, 0x75, 0x62,
            0x6E, 0x6F, 0x72, 0x6D, 0x61, 0x6C,
        0xF9, 0x04, 0x00,   // 0.000061988
        0x70,
            0x73, 0x75, 0x62, 0x6E, 0x6F, 0x72, 0x6D, 0x61, 0x6C, 0x20, 0x73,
            0x69, 0x6E, 0x67, 0x6C, 0x65,
        0xF9, 0x00, 0x00,
        0x03,
        0xF9, 0xC0, 0x00,    // -2
        0x04,
        0xF9, 0x7E, 0x00,    // qNaN
        0x05,
        0xF9, 0x7C, 0x01,    // sNaN
        0x06,
        0xF9, 0x7E, 0x0F,    // qNaN with payload 0x0f
        0x07,
        0xF9, 0x7C, 0x0F,    // sNaN with payload 0x0f

};


int32_t HalfPrecisionDecodeBasicTests()
{
    UsefulBufC HalfPrecision = UsefulBuf_FROM_BYTE_ARRAY_LITERAL(spExpectedHalf);

    QCBORDecodeContext DC;
    QCBORDecode_Init(&DC, HalfPrecision, 0);

    QCBORItem Item;

    QCBORDecode_GetNext(&DC, &Item);
    if(Item.uDataType != QCBOR_TYPE_MAP) {
        return -1;
    }

    QCBORDecode_GetNext(&DC, &Item);
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != 0.0F) {
        return -2;
    }

    QCBORDecode_GetNext(&DC, &Item);
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != INFINITY) {
        return -3;
    }

    QCBORDecode_GetNext(&DC, &Item);
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != -INFINITY) {
        return -4;
    }

    // TODO, is this really converting right? It is carrying payload, but
    // this confuses things.
    QCBORDecode_GetNext(&DC, &Item);
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || !isnan(Item.val.dfnum)) {
        return -5;
    }

    QCBORDecode_GetNext(&DC, &Item);
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != 1.0F) {
        return -6;
    }

    QCBORDecode_GetNext(&DC, &Item);
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != 0.333251953125F) {
        return -7;
    }

    QCBORDecode_GetNext(&DC, &Item);
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != 65504.0F) {
        return -8;
    }

    QCBORDecode_GetNext(&DC, &Item);
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != INFINITY) {
        return -9;
    }

    QCBORDecode_GetNext(&DC, &Item); // TODO: check this
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != 0.0000000596046448F) {
        return -10;
    }

    QCBORDecode_GetNext(&DC, &Item); // TODO: check this
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != 0.0000609755516F) {
        return -11;
    }

    QCBORDecode_GetNext(&DC, &Item); // TODO check this
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != 0.0000610351563F) {
        return -12;
    }

    QCBORDecode_GetNext(&DC, &Item);
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != 0) {
        return -13;
    }

    QCBORDecode_GetNext(&DC, &Item);
    if(Item.uDataType != QCBOR_TYPE_DOUBLE || Item.val.dfnum != -2.0F) {
        return -14;
    }

    // TODO: double check these four tests
    QCBORDecode_GetNext(&DC, &Item); // qNaN
    if(Item.uDataType != QCBOR_TYPE_DOUBLE ||
       UsefulBufUtil_CopyDoubleToUint64(Item.val.dfnum) != 0x7ff8000000000000ULL) {
        return -15;
    }
    QCBORDecode_GetNext(&DC, &Item); // sNaN
    if(Item.uDataType != QCBOR_TYPE_DOUBLE ||
       UsefulBufUtil_CopyDoubleToUint64(Item.val.dfnum) != 0x7ff0000000000001ULL) {
        return -16;
    }
    QCBORDecode_GetNext(&DC, &Item); // qNaN with payload 0x0f
    if(Item.uDataType != QCBOR_TYPE_DOUBLE ||
       UsefulBufUtil_CopyDoubleToUint64(Item.val.dfnum) != 0x7ff800000000000fULL) {
        return -17;
    }
    QCBORDecode_GetNext(&DC, &Item); // sNaN with payload 0x0f
    if(Item.uDataType != QCBOR_TYPE_DOUBLE ||
       UsefulBufUtil_CopyDoubleToUint64(Item.val.dfnum) != 0x7ff000000000000fULL) {
        return -18;
    }

    if(QCBORDecode_Finish(&DC)) {
        return -19;
    }

    return 0;
}




int32_t HalfPrecisionAgainstRFCCodeTest()
{
    for(uint32_t uHalfP = 0; uHalfP < 0xffff; uHalfP += 60) {
        unsigned char x[2];
        x[1] = (uint8_t)(uHalfP & 0xff);
        x[0] = (uint8_t)(uHalfP >> 8); // uHalfP is always less than 0xffff
        double d = decode_half(x);

        // Contruct the CBOR for the half-precision float by hand
        UsefulBuf_MAKE_STACK_UB(__xx, 3);
        UsefulOutBuf UOB;
        UsefulOutBuf_Init(&UOB, __xx);

        const uint8_t uHalfPrecInitialByte = (uint8_t)(HALF_PREC_FLOAT + (CBOR_MAJOR_TYPE_SIMPLE << 5)); // 0xf9
        UsefulOutBuf_AppendByte(&UOB, uHalfPrecInitialByte); // The initial byte for a half-precision float
        UsefulOutBuf_AppendUint16(&UOB, (uint16_t)uHalfP);

        // Now parse the hand-constructed CBOR. This will invoke the
        // conversion to a float
        QCBORDecodeContext DC;
        QCBORDecode_Init(&DC, UsefulOutBuf_OutUBuf(&UOB), 0);

        QCBORItem Item;

        QCBORDecode_GetNext(&DC, &Item);
        if(Item.uDataType != QCBOR_TYPE_DOUBLE) {
            return -1;
        }

        //printf("%04x  QCBOR:%15.15f  RFC: %15.15f (%8x)\n",
        //       uHalfP, Item.val.fnum, d , UsefulBufUtil_CopyFloatToUint32(d));

        if(isnan(d)) {
            // The RFC code uses the native instructions which may or may not
            // handle sNaN, qNaN and NaN payloads correctly. This test just
            // makes sure it is a NaN and doesn't worry about the type of NaN
            if(!isnan(Item.val.dfnum)) {
                return -3;
            }
        } else {
            if(Item.val.dfnum != d) {
                return -2;
            }
        }
    }
    return 0;
}


/*
 {"zero": 0.0,
  "negative zero": -0.0,
  "infinitity": Infinity,
  "negative infinitity": -Infinity,
  "NaN": NaN,
  "one": 1.0,
  "one third": 0.333251953125,
  "largest half-precision": 65504.0,
  "largest half-precision point one": 65504.1,
  "too-large half-precision": 65536.0,
  "smallest subnormal": 5.96046448e-8,
  "smallest normal": 0.00006103515261202119,
  "biggest subnormal": 0.00006103515625,
  "subnormal single": 4.00000646641519e-40,
  3: -2.0,
  "large single exp": 2.5521177519070385e+38,
  "too-large single exp": 5.104235503814077e+38,
  "biggest single with prec": 16777216.0,
  "first single with prec loss": 16777217.0,
  1: "fin"}
 */
static const uint8_t spExpectedSmallest[] = {
    0xB4, 0x64, 0x7A, 0x65, 0x72, 0x6F, 0xF9, 0x00, 0x00, 0x6D,
    0x6E, 0x65, 0x67, 0x61, 0x74, 0x69, 0x76, 0x65, 0x20, 0x7A,
    0x65, 0x72, 0x6F, 0xF9, 0x80, 0x00, 0x6A, 0x69, 0x6E, 0x66,
    0x69, 0x6E, 0x69, 0x74, 0x69, 0x74, 0x79, 0xF9, 0x7C, 0x00,
    0x73, 0x6E, 0x65, 0x67, 0x61, 0x74, 0x69, 0x76, 0x65, 0x20,
    0x69, 0x6E, 0x66, 0x69, 0x6E, 0x69, 0x74, 0x69, 0x74, 0x79,
    0xF9, 0xFC, 0x00, 0x63, 0x4E, 0x61, 0x4E, 0xF9, 0x7E, 0x00,
    0x63, 0x6F, 0x6E, 0x65, 0xF9, 0x3C, 0x00, 0x69, 0x6F, 0x6E,
    0x65, 0x20, 0x74, 0x68, 0x69, 0x72, 0x64, 0xF9, 0x35, 0x55,
    0x76, 0x6C, 0x61, 0x72, 0x67, 0x65, 0x73, 0x74, 0x20, 0x68,
    0x61, 0x6C, 0x66, 0x2D, 0x70, 0x72, 0x65, 0x63, 0x69, 0x73,
    0x69, 0x6F, 0x6E, 0xF9, 0x7B, 0xFF, 0x78, 0x20, 0x6C, 0x61,
    0x72, 0x67, 0x65, 0x73, 0x74, 0x20, 0x68, 0x61, 0x6C, 0x66,
    0x2D, 0x70, 0x72, 0x65, 0x63, 0x69, 0x73, 0x69, 0x6F, 0x6E,
    0x20, 0x70, 0x6F, 0x69, 0x6E, 0x74, 0x20, 0x6F, 0x6E, 0x65,
    0xFB, 0x40, 0xEF, 0xFC, 0x03, 0x33, 0x33, 0x33, 0x33, 0x78,
    0x18, 0x74, 0x6F, 0x6F, 0x2D, 0x6C, 0x61, 0x72, 0x67, 0x65,
    0x20, 0x68, 0x61, 0x6C, 0x66, 0x2D, 0x70, 0x72, 0x65, 0x63,
    0x69, 0x73, 0x69, 0x6F, 0x6E, 0xFA, 0x47, 0x80, 0x00, 0x00,
    0x72, 0x73, 0x6D, 0x61, 0x6C, 0x6C, 0x65, 0x73, 0x74, 0x20,
    0x73, 0x75, 0x62, 0x6E, 0x6F, 0x72, 0x6D, 0x61, 0x6C, 0xFB,
    0x3E, 0x70, 0x00, 0x00, 0x00, 0x1C, 0x5F, 0x68, 0x6F, 0x73,
    0x6D, 0x61, 0x6C, 0x6C, 0x65, 0x73, 0x74, 0x20, 0x6E, 0x6F,
    0x72, 0x6D, 0x61, 0x6C, 0xFA, 0x38, 0x7F, 0xFF, 0xFF, 0x71,
    0x62, 0x69, 0x67, 0x67, 0x65, 0x73, 0x74, 0x20, 0x73, 0x75,
    0x62, 0x6E, 0x6F, 0x72, 0x6D, 0x61, 0x6C, 0xF9, 0x04, 0x00,
    0x70, 0x73, 0x75, 0x62, 0x6E, 0x6F, 0x72, 0x6D, 0x61, 0x6C,
    0x20, 0x73, 0x69, 0x6E, 0x67, 0x6C, 0x65, 0xFB, 0x37, 0xC1,
    0x6C, 0x28, 0x00, 0x00, 0x00, 0x00, 0x03, 0xF9, 0xC0, 0x00,
    0x70, 0x6C, 0x61, 0x72, 0x67, 0x65, 0x20, 0x73, 0x69, 0x6E,
    0x67, 0x6C, 0x65, 0x20, 0x65, 0x78, 0x70, 0xFA, 0x7F, 0x40,
    0x00, 0x00, 0x74, 0x74, 0x6F, 0x6F, 0x2D, 0x6C, 0x61, 0x72,
    0x67, 0x65, 0x20, 0x73, 0x69, 0x6E, 0x67, 0x6C, 0x65, 0x20,
    0x65, 0x78, 0x70, 0xFB, 0x47, 0xF8, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x78, 0x18, 0x62, 0x69, 0x67, 0x67, 0x65, 0x73,
    0x74, 0x20, 0x73, 0x69, 0x6E, 0x67, 0x6C, 0x65, 0x20, 0x77,
    0x69, 0x74, 0x68, 0x20, 0x70, 0x72, 0x65, 0x63, 0xFA, 0x4B,
    0x80, 0x00, 0x00, 0x78, 0x1B, 0x66, 0x69, 0x72, 0x73, 0x74,
    0x20, 0x73, 0x69, 0x6E, 0x67, 0x6C, 0x65, 0x20, 0x77, 0x69,
    0x74, 0x68, 0x20, 0x70, 0x72, 0x65, 0x63, 0x20, 0x6C, 0x6F,
    0x73, 0x73, 0xFB, 0x41, 0x70, 0x00, 0x00, 0x10, 0x00, 0x00,
    0x00, 0x01, 0x63, 0x66, 0x69, 0x6E
};


int32_t DoubleAsSmallestTest()
{
    UsefulBuf_MAKE_STACK_UB(EncodedHalfsMem, 420);

#define QCBOREncode_AddDoubleAsSmallestToMap QCBOREncode_AddDoubleToMap
#define QCBOREncode_AddDoubleAsSmallestToMapN QCBOREncode_AddDoubleToMapN


    QCBOREncodeContext EC;
    QCBOREncode_Init(&EC, EncodedHalfsMem);
    // These are mostly from https://en.wikipedia.org/wiki/Half-precision_floating-point_format
    QCBOREncode_OpenMap(&EC);
    // 64                                   # text(4)
    //    7A65726F                          # "zero"
    // F9 0000                              # primitive(0)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "zero", 0.00);

    // 64                                   # text(4)
    //    7A65726F                          # "negative zero"
    // F9 8000                              # primitive(0)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "negative zero", -0.00);

    // 6A                                   # text(10)
    //    696E66696E6974697479              # "infinitity"
    // F9 7C00                              # primitive(31744)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "infinitity", INFINITY);

    // 73                                   # text(19)
    //    6E6567617469766520696E66696E6974697479 # "negative infinitity"
    // F9 FC00                              # primitive(64512)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "negative infinitity", -INFINITY);

    // 63                                   # text(3)
    //    4E614E                            # "NaN"
    // F9 7E00                              # primitive(32256)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "NaN", NAN);

    // TODO: test a few NaN variants

    // 63                                   # text(3)
    //    6F6E65                            # "one"
    // F9 3C00                              # primitive(15360)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "one", 1.0);

    // 69                                   # text(9)
    //    6F6E65207468697264                # "one third"
    // F9 3555                              # primitive(13653)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "one third", 0.333251953125);

    // 76                                   # text(22)
    //   6C6172676573742068616C662D707265636973696F6E # "largest half-precision"
    // F9 7BFF                              # primitive(31743)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "largest half-precision",65504.0);

    // 76                                   # text(22)
    //   6C6172676573742068616C662D707265636973696F6E # "largest half-precision"
    // F9 7BFF                              # primitive(31743)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "largest half-precision point one",65504.1);

    // Float 65536.0F is 0x47800000 in hex. It has an exponent of 16, which
    // is larger than 15, the largest half-precision exponent
    // 78 18                                # text(24)
    //    746F6F2D6C617267652068616C662D707265636973696F6E # "too-large half-precision"
    // FA 47800000                          # primitive(31743)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "too-large half-precision", 65536.0);

    // The smallest possible half-precision subnormal, but digitis are lost converting
    // to half, so this turns into a double
    // 72                                   # text(18)
    //    736D616C6C657374207375626E6F726D616C # "smallest subnormal"
    // FB 3E700000001C5F68                  # primitive(4499096027744984936)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "smallest subnormal", 0.0000000596046448);

    // The smallest possible half-precision snormal, but digitis are lost converting
    // to half, so this turns into a single TODO: confirm this is right
    // 6F                                   # text(15)
    //    736D616C6C657374206E6F726D616C    # "smallest normal"
    // FA 387FFFFF                          # primitive(947912703)
    // in hex single is 0x387fffff, exponent -15, significand 7fffff
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "smallest normal",    0.0000610351526F);

    // 71                                   # text(17)
    //    62696767657374207375626E6F726D616C # "biggest subnormal"
    // F9 0400                              # primitive(1024)
    // in hex single is 0x38800000, exponent -14, significand 0
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "biggest subnormal",  0.0000610351563F);

    // 70                                   # text(16)
    //    7375626E6F726D616C2073696E676C65  # "subnormal single"
    // FB 37C16C2800000000                  # primitive(4017611261645684736)
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "subnormal single", 4e-40F);

    // 03                                   # unsigned(3)
    // F9 C000                              # primitive(49152)
    QCBOREncode_AddDoubleAsSmallestToMapN(&EC, 3, -2.0);

    // 70                                   # text(16)
    //    6C617267652073696E676C6520657870  # "large single exp"
    // FA 7F400000                          # primitive(2134900736)
    // (0x01LL << (DOUBLE_NUM_SIGNIFICAND_BITS-1)) | ((127LL + DOUBLE_EXPONENT_BIAS) << DOUBLE_EXPONENT_SHIFT);
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "large single exp", 2.5521177519070385E+38); // Exponent fits  single

    // 74                                   # text(20)
    //    746F6F2D6C617267652073696E676C6520657870 # "too-large single exp"
    // FB 47F8000000000000                  # primitive(5185894970917126144)
    // (0x01LL << (DOUBLE_NUM_SIGNIFICAND_BITS-1)) | ((128LL + DOUBLE_EXPONENT_BIAS) << DOUBLE_EXPONENT_SHIFT);
    // Exponent too large for single
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "too-large single exp", 5.104235503814077E+38);

    // 66                                   # text(6)
    //    646664666465                      # "dfdfde"
    // FA 4B800000                          # primitive(1266679808)
    // Single with no precision loss
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "biggest single with prec", 16777216);

    // 78 18                                # text(24)
    //    626967676573742073696E676C6520776974682070726563 # "biggest single with prec"
    // FA 4B800000                          # primitive(1266679808)
    // Double becuase of precision loss
    QCBOREncode_AddDoubleAsSmallestToMap(&EC, "first single with prec loss", 16777217);

    // Just a convenient marker when cutting and pasting encoded CBOR
    QCBOREncode_AddSZStringToMapN(&EC, 1, "fin");

    QCBOREncode_CloseMap(&EC);

    UsefulBufC EncodedHalfs;
    int nReturn = QCBOREncode_Finish(&EC, &EncodedHalfs);
    if(nReturn) {
        return -1;
    }

    if(UsefulBuf_Compare(EncodedHalfs, UsefulBuf_FROM_BYTE_ARRAY_LITERAL(spExpectedSmallest))) {
        return -3;
    }

    return 0;
}



#ifdef NAN_EXPERIMENT
/*
 Code for checking what the double to float cast does with
 NaNs.  Not run as part of tests. Keep it around to
 be able to check various platforms and CPUs.
 */

#define DOUBLE_NUM_SIGNIFICAND_BITS (52)
#define DOUBLE_NUM_EXPONENT_BITS    (11)
#define DOUBLE_NUM_SIGN_BITS        (1)

#define DOUBLE_SIGNIFICAND_SHIFT    (0)
#define DOUBLE_EXPONENT_SHIFT       (DOUBLE_NUM_SIGNIFICAND_BITS)
#define DOUBLE_SIGN_SHIFT           (DOUBLE_NUM_SIGNIFICAND_BITS + DOUBLE_NUM_EXPONENT_BITS)

#define DOUBLE_SIGNIFICAND_MASK     (0xfffffffffffffULL) // The lower 52 bits
#define DOUBLE_EXPONENT_MASK        (0x7ffULL << DOUBLE_EXPONENT_SHIFT) // 11 bits of exponent
#define DOUBLE_SIGN_MASK            (0x01ULL << DOUBLE_SIGN_SHIFT) // 1 bit of sign
#define DOUBLE_QUIET_NAN_BIT        (0x01ULL << (DOUBLE_NUM_SIGNIFICAND_BITS-1))


static int NaNExperiments() {
    double dqNaN = UsefulBufUtil_CopyUint64ToDouble(DOUBLE_EXPONENT_MASK | DOUBLE_QUIET_NAN_BIT);
    double dsNaN = UsefulBufUtil_CopyUint64ToDouble(DOUBLE_EXPONENT_MASK | 0x01);
    double dqNaNPayload = UsefulBufUtil_CopyUint64ToDouble(DOUBLE_EXPONENT_MASK | DOUBLE_QUIET_NAN_BIT | 0xf00f);

    float f1 = (float)dqNaN;
    float f2 = (float)dsNaN;
    float f3 = (float)dqNaNPayload;


    uint32_t uqNaN = UsefulBufUtil_CopyFloatToUint32((float)dqNaN);
    uint32_t usNaN = UsefulBufUtil_CopyFloatToUint32((float)dsNaN);
    uint32_t uqNaNPayload = UsefulBufUtil_CopyFloatToUint32((float)dqNaNPayload);

    // Result of this on x86 is that every NaN is a qNaN. The intel
    // CVTSD2SS instruction ignores the NaN payload and even converts
    // a sNaN to a qNaN.

    return 0;
}
#endif