Is there a tool to know whether a value has an exact binary representation as a floating point variable?
Solution 1:
Here's a Python snippet that does exactly what you ask for; it needs Python 2.7 or Python 3.x. (Earlier versions of Python are less careful with floating-point conversions.)
import decimal, sys
input = sys.argv[1]
if decimal.Decimal(input) == float(input):
print("Exactly representable")
else:
print("Not exactly representable")
Usage: after saving the script under the name 'exactly_representable.py',
mdickinson$ python exactly_representable.py 1.25
Exactly representable
mdickinson$ python exactly_representable.py 0.1
Not exactly representable
mdickinson$ python exactly_representable.py 1e22
Exactly representable
mdickinson$ python exactly_representable.py 1e23
Not exactly representable
Solution 2:
I've written a decimal to float/double converter for fun and made it produce an extra output flag telling whether or not the resultant floating-point value represents the input decimal string exactly.
The main idea is very simple. Whenever truncation or rounding occurs during conversion, it's remembered.
The code is not the most efficient nor does it fully validate input for all possible problems (e.g. too large exponent), but it seems to do the job for well-formed decimal strings:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <limits.h>
#define DEBUG_PRINT 0
#ifndef MIN
#define MIN(A,B) (((A) <= (B)) ? (A) : (B))
#endif
#ifndef MAX
#define MAX(A,B) (((A) >= (B)) ? (A) : (B))
#endif
static
int ParseDecimal(const char* s,
int* pSign,
const char** ppIntStart,
const char** ppIntEnd,
const char** ppFrcStart,
const char** ppFrcEnd,
int* pExp)
{
int sign = 1;
const char* pIntStart = NULL;
const char* pIntEnd = NULL;
const char* pFrcStart = NULL;
const char* pFrcEnd = NULL;
int expSign = 1;
const char* pExpStart = NULL;
const char* pExpEnd = NULL;
const char* p;
int exp = 0;
if (s == NULL) return -1;
// Parse the sign and the integer part
if (*s == '-') sign = -1, s++;
else if (*s == '+') s++;
while (*s && *s != '.' && *s != 'e' && *s != 'E')
{
if (*s < '0' || *s > '9') return -1;
if (pIntStart == NULL) pIntStart = s;
pIntEnd = s++;
}
// Parse the fractional part
if (*s == '.')
{
s++;
while (*s && *s != 'e' && *s != 'E')
{
if (*s < '0' || *s > '9') return -1;
if (pFrcStart == NULL) pFrcStart = s;
pFrcEnd = s++;
}
}
if (pIntStart == NULL && pFrcStart == NULL) return -1;
// Parse the exponent
if (*s == 'e' || *s == 'E')
{
s++;
if (*s == '-') expSign = -1, s++;
else if (*s == '+') s++;
if (!*s) return -1;
while (*s)
{
if (*s < '0' || *s > '9') return -1;
if (pExpStart == NULL) pExpStart = s;
pExpEnd = s++;
}
}
// Calculate the exponent
for (p = pExpStart; p && p <= pExpEnd; p++)
exp = exp * 10 + *p - '0';
exp *= expSign;
// Skip any trailing and leading zeroes
// in the fractional and integer parts
if (pFrcStart != NULL)
{
exp -= pFrcEnd + 1 - pFrcStart;
if (pIntStart == NULL)
while (pFrcStart < pFrcEnd && *pFrcStart == '0') pFrcStart++;
while (pFrcEnd > pFrcStart && *pFrcEnd == '0') pFrcEnd--, exp++;
if (*pFrcEnd == '0' && pIntStart != NULL) pFrcStart = pFrcEnd = NULL, exp++;
}
if (pIntStart != NULL)
{
if (pFrcStart == NULL)
while (pIntEnd > pIntStart && *pIntEnd == '0') pIntEnd--, exp++;
while (pIntStart < pIntEnd && *pIntStart == '0') pIntStart++;
if (*pIntStart == '0' && pFrcStart != NULL)
{
pIntStart = pIntEnd = NULL;
while (pFrcStart < pFrcEnd && *pFrcStart == '0') pFrcStart++;
}
}
if ((pIntStart != NULL && *pIntStart == '0') ||
(pFrcEnd != NULL && *pFrcEnd == '0'))
{
exp = 0;
}
*pSign = sign;
*ppIntStart = pIntStart;
*ppIntEnd = pIntEnd;
*ppFrcStart = pFrcStart;
*ppFrcEnd = pFrcEnd;
*pExp = exp;
return 0;
}
static
void ChainMultiplyAdd(unsigned char* pChain,
size_t ChainLen,
unsigned char Multiplier,
unsigned char Addend)
{
unsigned carry = Addend;
while (ChainLen--)
{
carry += *pChain * Multiplier;
*pChain++ = (unsigned char)(carry & 0xFF);
carry >>= 8;
}
}
static
void ChainDivide(unsigned char* pChain,
size_t ChainLen,
unsigned char Divisor,
unsigned char* pRemainder)
{
unsigned remainder = 0;
while (ChainLen)
{
remainder += pChain[ChainLen - 1];
pChain[ChainLen - 1] = remainder / Divisor;
remainder = (remainder % Divisor) << 8;
ChainLen--;
}
if (pRemainder != NULL)
*pRemainder = (unsigned char)(remainder >> 8);
}
int DecimalToIeee754Binary(const char* s,
unsigned FractionBitCnt,
unsigned ExponentBitCnt,
int* pInexact,
unsigned long long* pFloat)
{
const char* pIntStart;
const char* pIntEnd;
const char* pFrcStart;
const char* pFrcEnd;
const char* p;
int sign;
int exp;
int tmp;
size_t numDecDigits;
size_t denDecDigits;
size_t numBinDigits;
size_t numBytes;
unsigned char* pNum = NULL;
unsigned char remainder;
int binExp = 0;
int inexact = 0;
int lastInexact = 0;
if (FractionBitCnt < 3 ||
ExponentBitCnt < 3 ||
FractionBitCnt >= CHAR_BIT * sizeof(*pFloat) ||
ExponentBitCnt >= CHAR_BIT * sizeof(*pFloat) ||
FractionBitCnt + ExponentBitCnt >= CHAR_BIT * sizeof(*pFloat))
{
return -1;
}
tmp = ParseDecimal(s,
&sign,
&pIntStart,
&pIntEnd,
&pFrcStart,
&pFrcEnd,
&exp);
if (tmp) return tmp;
numDecDigits = ((pIntStart != NULL) ? pIntEnd + 1 - pIntStart : 0) +
((pFrcStart != NULL) ? pFrcEnd + 1 - pFrcStart : 0) +
((exp >= 0) ? exp : 0);
denDecDigits = 1 + ((exp < 0) ? -exp : 0);
#if DEBUG_PRINT
printf("%s ", s);
printf("%c", "- +"[1+sign]);
for (p = pIntStart; p && p <= pIntEnd; p++) printf("%c", *p);
for (p = pFrcStart; p && p <= pFrcEnd; p++) printf("%c", *p);
printf(" E %d", exp);
printf(" %zu/%zu ", numDecDigits, denDecDigits);
// fflush(stdout);
printf("\n");
#endif
// 10/3=3.3(3) > log2(10)~=3.32
if (exp >= 0)
numBinDigits = MAX((numDecDigits * 10 + 2) / 3,
FractionBitCnt + 1);
else
numBinDigits = MAX((numDecDigits * 10 + 2) / 3,
(denDecDigits * 10 + 2) / 3 + FractionBitCnt + 1 + 1);
numBytes = (numBinDigits + 7) / 8;
pNum = malloc(numBytes);
if (pNum == NULL) return -2;
memset(pNum, 0, numBytes);
// Convert the numerator to binary
for (p = pIntStart; p && p <= pIntEnd; p++)
ChainMultiplyAdd(pNum, numBytes, 10, *p - '0');
for (p = pFrcStart; p && p <= pFrcEnd; p++)
ChainMultiplyAdd(pNum, numBytes, 10, *p - '0');
for (tmp = exp; tmp > 0; tmp--)
ChainMultiplyAdd(pNum, numBytes, 10, 0);
#if DEBUG_PRINT
printf("num : ");
for (p = pNum + numBytes - 1; p >= (char*)pNum; p--)
printf("%02X", (unsigned char)*p);
printf("\n");
#endif
// If the denominator isn't 1, divide the numerator by the denominator
// getting at least FractionBitCnt+2 significant bits of quotient
if (exp < 0)
{
binExp = -(int)(numBinDigits - (numDecDigits * 10 + 2) / 3);
for (tmp = binExp; tmp < 0; tmp++)
ChainMultiplyAdd(pNum, numBytes, 2, 0);
#if DEBUG_PRINT
printf("num <<: ");
for (p = pNum + numBytes - 1; p >= (char*)pNum; p--)
printf("%02X", (unsigned char)*p);
printf("\n");
#endif
for (tmp = exp; tmp < 0; tmp++)
ChainDivide(pNum, numBytes, 10, &remainder),
lastInexact = inexact, inexact |= !!remainder;
}
#if DEBUG_PRINT
for (p = pNum + numBytes - 1; p >= (char*)pNum; p--)
printf("%02X", (unsigned char)*p);
printf(" * 2^%d (%c)", binExp, "ei"[inexact]);
printf("\n");
#endif
// Find the most significant bit and normalize the mantissa
// by shifting it left
for (tmp = numBytes - 1; tmp >= 0 && !pNum[tmp]; tmp--);
if (tmp >= 0)
{
tmp = tmp * 8 + 7;
while (!(pNum[tmp / 8] & (1 << tmp % 8))) tmp--;
while (tmp < (int)FractionBitCnt)
ChainMultiplyAdd(pNum, numBytes, 2, 0), binExp--, tmp++;
}
// Find the most significant bit and normalize the mantissa
// by shifting it right
do
{
remainder = 0;
for (tmp = numBytes - 1; tmp >= 0 && !pNum[tmp]; tmp--);
if (tmp >= 0)
{
tmp = tmp * 8 + 7;
while (!(pNum[tmp / 8] & (1 << tmp % 8))) tmp--;
while (tmp > (int)FractionBitCnt)
ChainDivide(pNum, numBytes, 2, &remainder),
lastInexact = inexact, inexact |= !!remainder, binExp++, tmp--;
while (binExp < 2 - (1 << ((int)ExponentBitCnt - 1)) - (int)FractionBitCnt)
ChainDivide(pNum, numBytes, 2, &remainder),
lastInexact = inexact, inexact |= !!remainder, binExp++;
}
// Round to nearest even
remainder &= (lastInexact | (pNum[0] & 1));
if (remainder)
ChainMultiplyAdd(pNum, numBytes, 1, 1);
} while (remainder);
#if DEBUG_PRINT
for (p = pNum + numBytes - 1; p >= (char*)pNum; p--)
printf("%02X", (unsigned char)*p);
printf(" * 2^%d", binExp);
printf("\n");
#endif
// Collect the result's mantissa
*pFloat = 0;
while (tmp >= 0)
{
*pFloat <<= 8;
*pFloat |= pNum[tmp / 8];
tmp -= 8;
}
// Collect the result's exponent
binExp += (1 << ((int)ExponentBitCnt - 1)) - 1 + (int)FractionBitCnt;
if (!(*pFloat & (1ull << FractionBitCnt))) binExp = 0; // Subnormal or 0
*pFloat &= ~(1ull << FractionBitCnt);
if (binExp >= (1 << (int)ExponentBitCnt) - 1)
binExp = (1 << (int)ExponentBitCnt) - 1, *pFloat = 0, inexact |= 1; // Infinity
*pFloat |= (unsigned long long)binExp << FractionBitCnt;
// Collect the result's sign
*pFloat |= (unsigned long long)(sign < 0) <<
(ExponentBitCnt + FractionBitCnt);
free(pNum);
*pInexact = inexact;
return 0;
}
#define TEST_ENTRY(n) { #n, n, n##f }
#define TEST_ENTRYI(n) { #n, n, n }
struct
{
const char* Decimal;
double Dbl;
float Flt;
} const testData[] =
{
TEST_ENTRYI(0),
TEST_ENTRYI(000),
TEST_ENTRY(00.),
TEST_ENTRY(.00),
TEST_ENTRY(00.00),
TEST_ENTRYI(1),
TEST_ENTRY(10e-1),
TEST_ENTRY(.1e1),
TEST_ENTRY(.01e2),
TEST_ENTRY(00.00100e3),
TEST_ENTRYI(12),
TEST_ENTRY(12.),
TEST_ENTRYI(+12),
TEST_ENTRYI(-12),
TEST_ENTRY(.12),
TEST_ENTRY(+.12),
TEST_ENTRY(-.12),
TEST_ENTRY(12.34),
TEST_ENTRY(+12.34),
TEST_ENTRY(-12.34),
TEST_ENTRY(00.100),
TEST_ENTRY(00100.),
TEST_ENTRY(00100.00100),
TEST_ENTRY(1e4),
TEST_ENTRY(0.5),
TEST_ENTRY(0.6),
TEST_ENTRY(0.25),
TEST_ENTRY(0.26),
TEST_ENTRY(0.125),
TEST_ENTRY(0.126),
TEST_ENTRY(0.0625),
TEST_ENTRY(0.0624),
TEST_ENTRY(0.03125),
TEST_ENTRY(0.03124),
TEST_ENTRY(1e23),
TEST_ENTRY(1E-23),
TEST_ENTRY(1e+23),
TEST_ENTRY(12.34E56),
TEST_ENTRY(+12.34E+56),
TEST_ENTRY(-12.34e-56),
TEST_ENTRY(+.12E+34),
TEST_ENTRY(-.12e-34),
TEST_ENTRY(3.4028234e38),
TEST_ENTRY(3.4028235e38),
TEST_ENTRY(3.4028236e38),
TEST_ENTRY(1.7976931348623158e308),
TEST_ENTRY(1.7976931348623159e308),
TEST_ENTRY(1e1000),
TEST_ENTRY(-1.7976931348623158e308),
TEST_ENTRY(-1.7976931348623159e308),
TEST_ENTRY(2.2250738585072014e-308),
TEST_ENTRY(2.2250738585072013e-308),
TEST_ENTRY(2.2250738585072012e-308),
TEST_ENTRY(2.2250738585072011e-308),
TEST_ENTRY(4.9406564584124654e-324),
TEST_ENTRY(2.4703282292062328e-324),
TEST_ENTRY(2.4703282292062327e-324),
TEST_ENTRY(-4.9406564584124654e-325),
TEST_ENTRY(1e-1000),
// Extra test data from Vern Paxson's paper
// "A Program for Testing IEEE Decimal–Binary Conversion"
TEST_ENTRY(5e-20 ),
TEST_ENTRY(67e+14 ),
TEST_ENTRY(985e+15 ),
TEST_ENTRY(7693e-42 ),
TEST_ENTRY(55895e-16 ),
TEST_ENTRY(996622e-44 ),
TEST_ENTRY(7038531e-32 ),
TEST_ENTRY(60419369e-46 ),
TEST_ENTRY(702990899e-20 ),
TEST_ENTRY(6930161142e-48 ),
TEST_ENTRY(25933168707e+13 ),
TEST_ENTRY(596428896559e+20 ),
TEST_ENTRY(3e-23 ),
TEST_ENTRY(57e+18 ),
TEST_ENTRY(789e-35 ),
TEST_ENTRY(2539e-18 ),
TEST_ENTRY(76173e+28 ),
TEST_ENTRY(887745e-11 ),
TEST_ENTRY(5382571e-37 ),
TEST_ENTRY(82381273e-35 ),
TEST_ENTRY(750486563e-38 ),
TEST_ENTRY(3752432815e-39 ),
TEST_ENTRY(75224575729e-45 ),
TEST_ENTRY(459926601011e+15 ),
TEST_ENTRY(7e-27 ),
TEST_ENTRY(37e-29 ),
TEST_ENTRY(743e-18 ),
TEST_ENTRY(7861e-33 ),
TEST_ENTRY(46073e-30 ),
TEST_ENTRY(774497e-34 ),
TEST_ENTRY(8184513e-33 ),
TEST_ENTRY(89842219e-28 ),
TEST_ENTRY(449211095e-29 ),
TEST_ENTRY(8128913627e-40 ),
TEST_ENTRY(87365670181e-18 ),
TEST_ENTRY(436828350905e-19 ),
TEST_ENTRY(5569902441849e-49 ),
TEST_ENTRY(60101945175297e-32 ),
TEST_ENTRY(754205928904091e-51 ),
TEST_ENTRY(5930988018823113e-37 ),
TEST_ENTRY(51417459976130695e-27 ),
TEST_ENTRY(826224659167966417e-41 ),
TEST_ENTRY(9612793100620708287e-57 ),
TEST_ENTRY(93219542812847969081e-39 ),
TEST_ENTRY(544579064588249633923e-48 ),
TEST_ENTRY(4985301935905831716201e-48),
TEST_ENTRY(9e+26 ),
TEST_ENTRY(79e-8 ),
TEST_ENTRY(393e+26 ),
TEST_ENTRY(9171e-40 ),
TEST_ENTRY(56257e-16 ),
TEST_ENTRY(281285e-17 ),
TEST_ENTRY(4691113e-43 ),
TEST_ENTRY(29994057e-15 ),
TEST_ENTRY(834548641e-46 ),
TEST_ENTRY(1058695771e-47 ),
TEST_ENTRY(87365670181e-18 ),
TEST_ENTRY(872580695561e-36 ),
TEST_ENTRY(6638060417081e-51 ),
TEST_ENTRY(88473759402752e-52 ),
TEST_ENTRY(412413848938563e-27 ),
TEST_ENTRY(5592117679628511e-48 ),
TEST_ENTRY(83881765194427665e-50 ),
TEST_ENTRY(638632866154697279e-35 ),
TEST_ENTRY(3624461315401357483e-53 ),
TEST_ENTRY(75831386216699428651e-30 ),
TEST_ENTRY(356645068918103229683e-42 ),
TEST_ENTRY(7022835002724438581513e-33),
};
int main(void)
{
int i;
int errors = 0;
for (i = 0; i < sizeof(testData) / sizeof(testData[0]); i++)
{
unsigned long long fd;
unsigned long long ff;
unsigned long long f = 0;
unsigned long long d = 0;
int inexactf = 1;
int inexactd = 1;
int resf;
int resd;
int cmpf;
int cmpd;
memcpy(&d, &testData[i].Dbl, MIN(sizeof(d), sizeof(testData[i].Dbl)));
memcpy(&f, &testData[i].Flt, MIN(sizeof(f), sizeof(testData[i].Flt)));
resd = DecimalToIeee754Binary(testData[i].Decimal, 52, 11, &inexactd, &fd);
resf = DecimalToIeee754Binary(testData[i].Decimal, 23, 8, &inexactf, &ff);
cmpd = !!memcmp(&d, &fd, MIN(sizeof(d), sizeof(testData[i].Dbl)));
cmpf = !!memcmp(&f, &ff, MIN(sizeof(f), sizeof(testData[i].Flt)));
errors += !!resd + !!resf + !!cmpd + !!cmpf;
printf("%26s %c= 0x%016llX %c= 0x%016llX\n",
testData[i].Decimal,
"!="[!inexactd],
resd ? 0xBADBADBADBADBADBULL : fd,
"!="[!memcmp(&d, &fd, MIN(sizeof(d), sizeof(testData[i].Dbl)))],
d);
printf("%26s %c= 0x%08llX %c= 0x%08llX\n",
testData[i].Decimal,
"!="[!inexactf],
resf ? 0xBADBADBADBADBADBULL : ff,
"!="[!memcmp(&f, &ff, MIN(sizeof(f), sizeof(testData[i].Flt)))],
f);
}
printf("errors: %d\n", errors);
return 0;
}
Output (on x86 PC in 32-bit mode under Windows XP):
0 == 0x0000000000000000 == 0x0000000000000000
0 == 0x00000000 == 0x00000000
000 == 0x0000000000000000 == 0x0000000000000000
000 == 0x00000000 == 0x00000000
00. == 0x0000000000000000 == 0x0000000000000000
00. == 0x00000000 == 0x00000000
.00 == 0x0000000000000000 == 0x0000000000000000
.00 == 0x00000000 == 0x00000000
00.00 == 0x0000000000000000 == 0x0000000000000000
00.00 == 0x00000000 == 0x00000000
1 == 0x3FF0000000000000 == 0x3FF0000000000000
1 == 0x3F800000 == 0x3F800000
10e-1 == 0x3FF0000000000000 == 0x3FF0000000000000
10e-1 == 0x3F800000 == 0x3F800000
.1e1 == 0x3FF0000000000000 == 0x3FF0000000000000
.1e1 == 0x3F800000 == 0x3F800000
.01e2 == 0x3FF0000000000000 == 0x3FF0000000000000
.01e2 == 0x3F800000 == 0x3F800000
00.00100e3 == 0x3FF0000000000000 == 0x3FF0000000000000
00.00100e3 == 0x3F800000 == 0x3F800000
12 == 0x4028000000000000 == 0x4028000000000000
12 == 0x41400000 == 0x41400000
12. == 0x4028000000000000 == 0x4028000000000000
12. == 0x41400000 == 0x41400000
+12 == 0x4028000000000000 == 0x4028000000000000
+12 == 0x41400000 == 0x41400000
-12 == 0xC028000000000000 == 0xC028000000000000
-12 == 0xC1400000 == 0xC1400000
.12 != 0x3FBEB851EB851EB8 == 0x3FBEB851EB851EB8
.12 != 0x3DF5C28F == 0x3DF5C28F
+.12 != 0x3FBEB851EB851EB8 == 0x3FBEB851EB851EB8
+.12 != 0x3DF5C28F == 0x3DF5C28F
-.12 != 0xBFBEB851EB851EB8 == 0xBFBEB851EB851EB8
-.12 != 0xBDF5C28F == 0xBDF5C28F
12.34 != 0x4028AE147AE147AE == 0x4028AE147AE147AE
12.34 != 0x414570A4 == 0x414570A4
+12.34 != 0x4028AE147AE147AE == 0x4028AE147AE147AE
+12.34 != 0x414570A4 == 0x414570A4
-12.34 != 0xC028AE147AE147AE == 0xC028AE147AE147AE
-12.34 != 0xC14570A4 == 0xC14570A4
00.100 != 0x3FB999999999999A == 0x3FB999999999999A
00.100 != 0x3DCCCCCD == 0x3DCCCCCD
00100. == 0x4059000000000000 == 0x4059000000000000
00100. == 0x42C80000 == 0x42C80000
00100.00100 != 0x40590010624DD2F2 == 0x40590010624DD2F2
00100.00100 != 0x42C80083 == 0x42C80083
1e4 == 0x40C3880000000000 == 0x40C3880000000000
1e4 == 0x461C4000 == 0x461C4000
0.5 == 0x3FE0000000000000 == 0x3FE0000000000000
0.5 == 0x3F000000 == 0x3F000000
0.6 != 0x3FE3333333333333 == 0x3FE3333333333333
0.6 != 0x3F19999A == 0x3F19999A
0.25 == 0x3FD0000000000000 == 0x3FD0000000000000
0.25 == 0x3E800000 == 0x3E800000
0.26 != 0x3FD0A3D70A3D70A4 == 0x3FD0A3D70A3D70A4
0.26 != 0x3E851EB8 == 0x3E851EB8
0.125 == 0x3FC0000000000000 == 0x3FC0000000000000
0.125 == 0x3E000000 == 0x3E000000
0.126 != 0x3FC020C49BA5E354 == 0x3FC020C49BA5E354
0.126 != 0x3E010625 == 0x3E010625
0.0625 == 0x3FB0000000000000 == 0x3FB0000000000000
0.0625 == 0x3D800000 == 0x3D800000
0.0624 != 0x3FAFF2E48E8A71DE == 0x3FAFF2E48E8A71DE
0.0624 != 0x3D7F9724 == 0x3D7F9724
0.03125 == 0x3FA0000000000000 == 0x3FA0000000000000
0.03125 == 0x3D000000 == 0x3D000000
0.03124 != 0x3F9FFD60E94EE393 == 0x3F9FFD60E94EE393
0.03124 != 0x3CFFEB07 == 0x3CFFEB07
1e23 != 0x44B52D02C7E14AF6 == 0x44B52D02C7E14AF6
1e23 != 0x65A96816 == 0x65A96816
1E-23 != 0x3B282DB34012B251 == 0x3B282DB34012B251
1E-23 != 0x19416D9A == 0x19416D9A
1e+23 != 0x44B52D02C7E14AF6 == 0x44B52D02C7E14AF6
1e+23 != 0x65A96816 == 0x65A96816
12.34E56 != 0x4BC929C7D37D0D30 == 0x4BC929C7D37D0D30
12.34E56 != 0x7F800000 == 0x7F800000
+12.34E+56 != 0x4BC929C7D37D0D30 == 0x4BC929C7D37D0D30
+12.34E+56 != 0x7F800000 == 0x7F800000
-12.34e-56 != 0xB48834C13CBF331D == 0xB48834C13CBF331D
-12.34e-56 != 0x80000000 == 0x80000000
+.12E+34 != 0x46CD95108F882522 == 0x46CD95108F882522
+.12E+34 != 0x766CA884 == 0x766CA884
-.12e-34 != 0xB8AFE6C6DCC3C5AC == 0xB8AFE6C6DCC3C5AC
-.12e-34 != 0x857F3637 == 0x857F3637
3.4028234e38 != 0x47EFFFFFD586B834 == 0x47EFFFFFD586B834
3.4028234e38 != 0x7F7FFFFF == 0x7F7FFFFF
3.4028235e38 != 0x47EFFFFFE54DAFF8 == 0x47EFFFFFE54DAFF8
3.4028235e38 != 0x7F7FFFFF == 0x7F7FFFFF
3.4028236e38 != 0x47EFFFFFF514A7BC == 0x47EFFFFFF514A7BC
3.4028236e38 != 0x7F800000 == 0x7F800000
1.7976931348623158e308 != 0x7FEFFFFFFFFFFFFF == 0x7FEFFFFFFFFFFFFF
1.7976931348623158e308 != 0x7F800000 == 0x7F800000
1.7976931348623159e308 != 0x7FF0000000000000 == 0x7FF0000000000000
1.7976931348623159e308 != 0x7F800000 == 0x7F800000
1e1000 != 0x7FF0000000000000 == 0x7FF0000000000000
1e1000 != 0x7F800000 == 0x7F800000
-1.7976931348623158e308 != 0xFFEFFFFFFFFFFFFF == 0xFFEFFFFFFFFFFFFF
-1.7976931348623158e308 != 0xFF800000 == 0xFF800000
-1.7976931348623159e308 != 0xFFF0000000000000 == 0xFFF0000000000000
-1.7976931348623159e308 != 0xFF800000 == 0xFF800000
2.2250738585072014e-308 != 0x0010000000000000 == 0x0010000000000000
2.2250738585072014e-308 != 0x00000000 == 0x00000000
2.2250738585072013e-308 != 0x0010000000000000 == 0x0010000000000000
2.2250738585072013e-308 != 0x00000000 == 0x00000000
2.2250738585072012e-308 != 0x0010000000000000 == 0x0010000000000000
2.2250738585072012e-308 != 0x00000000 == 0x00000000
2.2250738585072011e-308 != 0x000FFFFFFFFFFFFF == 0x000FFFFFFFFFFFFF
2.2250738585072011e-308 != 0x00000000 == 0x00000000
4.9406564584124654e-324 != 0x0000000000000001 == 0x0000000000000001
4.9406564584124654e-324 != 0x00000000 == 0x00000000
2.4703282292062328e-324 != 0x0000000000000001 == 0x0000000000000001
2.4703282292062328e-324 != 0x00000000 == 0x00000000
2.4703282292062327e-324 != 0x0000000000000000 == 0x0000000000000000
2.4703282292062327e-324 != 0x00000000 == 0x00000000
-4.9406564584124654e-325 != 0x8000000000000000 == 0x8000000000000000
-4.9406564584124654e-325 != 0x80000000 == 0x80000000
1e-1000 != 0x0000000000000000 == 0x0000000000000000
1e-1000 != 0x00000000 == 0x00000000
5e-20 != 0x3BED83C94FB6D2AC == 0x3BED83C94FB6D2AC
5e-20 != 0x1F6C1E4A == 0x1F6C1E4A
67e+14 == 0x4337CD9D4FFEC000 == 0x4337CD9D4FFEC000
67e+14 != 0x59BE6CEA == 0x59BE6CEA
985e+15 == 0x43AB56D88FFF8500 == 0x43AB56D88FFF8500
985e+15 != 0x5D5AB6C4 == 0x5D5AB6C4
7693e-42 != 0x3804F13D0FFFE4A1 == 0x3804F13D0FFFE4A1
7693e-42 != 0x0053C4F4 == 0x0053C4F4
55895e-16 != 0x3D989537AFFFFFE1 == 0x3D989537AFFFFFE1
55895e-16 != 0x2CC4A9BD == 0x2CC4A9BD
996622e-44 != 0x380B21710FFFFFFB == 0x380B21710FFFFFFB
996622e-44 != 0x006C85C4 == 0x006C85C4
7038531e-32 != 0x3AB5C87FB0000000 == 0x3AB5C87FB0000000
7038531e-32 != 0x15AE43FD == 0x15AE43FD
60419369e-46 != 0x3800729D90000000 == 0x3800729D90000000
60419369e-46 != 0x0041CA76 == 0x0041CA76
702990899e-20 != 0x3D9EEAF950000000 == 0x3D9EEAF950000000
702990899e-20 != 0x2CF757CA == 0x2CF757CA
6930161142e-48 != 0x3802DD9E10000000 == 0x3802DD9E10000000
6930161142e-48 != 0x004B7678 == 0x004B7678
25933168707e+13 != 0x44CB753310000000 == 0x44CB753310000000
25933168707e+13 != 0x665BA998 == 0x665BA998
596428896559e+20 != 0x4687866490000000 == 0x4687866490000000
596428896559e+20 != 0x743C3324 == 0x743C3324
3e-23 != 0x3B422246700E05BD == 0x3B422246700E05BD
3e-23 != 0x1A111234 == 0x1A111234
57e+18 == 0x4408B84570022A20 == 0x4408B84570022A20
57e+18 != 0x6045C22C == 0x6045C22C
789e-35 != 0x39447BCDF000340C == 0x39447BCDF000340C
789e-35 != 0x0A23DE70 == 0x0A23DE70
...
errors: 0
The first == or != on each line of the output tells whether or not the obtained float/double represents the decimal input exactly.
The second == or != tells whether or not the calculated float/double matches the one generated by the compiler. The first hex number is from DecimalToIeee754Binary() and the second is from the compiler.
UPD: The code was compiled with gcc 4.6.2 and Open Watcom C/C++ 1.9.