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Ok, ok, I've fixed gradual underflow on packing too. 

Still don't know what to do with Inf/NaN, so I raise an exception on
pack(), and something random decided by ldexp() will happen on
unpack().
This commit is contained in:
Guido van Rossum 1997-01-02 23:23:20 +00:00
parent 6083f0e9ce
commit 4ccc531f34
1 changed files with 47 additions and 45 deletions
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92
Modules/structmodule.c
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@ -207,7 +207,7 @@ get_ulong(v, p)
Point Arithmetic). See the following URL:
http://www.psc.edu/general/software/packages/ieee/ieee.html */
/* XXX Signed zero, infinity, underflow, NaN are not handled quite right? */
/* XXX Inf/NaN are not handled quite right (but underflow is!) */
static int
pack_float(x, p, incr)
@ -217,8 +217,8 @@ pack_float(x, p, incr)
{
int s;
int e;
double fl;
long f;
double f;
long fbits;
if (x < 0) {
s = 1;
@ -226,13 +226,15 @@ pack_float(x, p, incr)
}
else
s = 0;
fl = frexp(x, &e);
/* Normalize fl to be in the range [1.0, 2.0) */
if (0.5 <= fl && fl < 1.0) {
fl *= 2.0;
f = frexp(x, &e);
/* Normalize f to be in the range [1.0, 2.0) */
if (0.5 <= f && f < 1.0) {
f *= 2.0;
e--;
}
else if (fl == 0.0) {
else if (f == 0.0) {
e = 0;
}
else {
@ -240,41 +242,40 @@ pack_float(x, p, incr)
"frexp() result out of range");
return -1;
}
e += 127;
if (e >= 255) {
/* XXX 255 itself is reserved for Inf/NaN */
if (e >= 128) {
/* XXX 128 itself is reserved for Inf/NaN */
PyErr_SetString(PyExc_OverflowError,
"float too large to pack with f format");
return -1;
}
else if (e <= 0) {
/* XXX Underflow -- could do better, but who cares? */
fl = 0.0;
else if (e < -126) {
/* Gradual underflow */
f = ldexp(f, 126 + e);
e = 0;
}
if (fl == 0.0) {
f = 0;
}
else {
fl -= 1.0; /* Get rid of leading 1 */
fl *= 8388608.0; /* 2**23 */
f = (long) floor(fl + 0.5); /* Round */
e += 127;
f -= 1.0; /* Get rid of leading 1 */
}
f *= 8388608.0; /* 2**23 */
fbits = (long) floor(f + 0.5); /* Round */
/* First byte */
*p = (s<<7) | (e>>1);
p += incr;
/* Second byte */
*p = ((e&1)<<7) | (f>>16);
*p = ((e&1)<<7) | (fbits>>16);
p += incr;
/* Third byte */
*p = (f>>8) & 0xFF;
*p = (fbits>>8) & 0xFF;
p += incr;
/* Fourth byte */
*p = f&0xFF;
*p = fbits&0xFF;
/* Done */
return 0;
@ -288,7 +289,7 @@ pack_double(x, p, incr)
{
int s;
int e;
double fl;
double f;
long fhi, flo;
if (x < 0) {
@ -297,13 +298,15 @@ pack_double(x, p, incr)
}
else
s = 0;
fl = frexp(x, &e);
/* Normalize fl to be in the range [1.0, 2.0) */
if (0.5 <= fl && fl < 1.0) {
fl *= 2.0;
f = frexp(x, &e);
/* Normalize f to be in the range [1.0, 2.0) */
if (0.5 <= f && f < 1.0) {
f *= 2.0;
e--;
}
else if (fl == 0.0) {
else if (f == 0.0) {
e = 0;
}
else {
@ -311,31 +314,30 @@ pack_double(x, p, incr)
"frexp() result out of range");
return -1;
}
e += 1023;
if (e >= 2047) {
/* XXX 2047 itself is reserved for Inf/NaN */
if (e >= 1024) {
/* XXX 1024 itself is reserved for Inf/NaN */
PyErr_SetString(PyExc_OverflowError,
"float too large to pack with d format");
return -1;
}
else if (e <= 0) {
/* XXX Underflow -- could do better, but who cares? */
fl = 0.0;
else if (e < -1022) {
/* Gradual underflow */
f = ldexp(f, 1022 + e);
e = 0;
}
if (fl == 0.0) {
fhi = flo = 0;
}
else {
/* fhi receives the high 28 bits; flo the low 24 bits */
fl -= 1.0;
fl *= 268435456.0; /* 2**28 */
fhi = (long) floor(fl); /* Truncate */
fl -= (double)fhi;
fl *= 16777216.0; /* 2**24 */
flo = (long) floor(fl + 0.5); /* Round */
e += 1023;
f -= 1.0; /* Get rid of leading 1 */
}
/* fhi receives the high 28 bits; flo the low 24 bits (== 52 bits) */
f *= 268435456.0; /* 2**28 */
fhi = (long) floor(f); /* Truncate */
f -= (double)fhi;
f *= 16777216.0; /* 2**24 */
flo = (long) floor(f + 0.5); /* Round */
/* First byte */
*p = (s<<7) | (e>>4);
p += incr;