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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: Point Arithmetic). See the following URL:
http://www.psc.edu/general/software/packages/ieee/ieee.html */ 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 static int
pack_float(x, p, incr) pack_float(x, p, incr)
@ -217,8 +217,8 @@ pack_float(x, p, incr)
{ {
int s; int s;
int e; int e;
double fl; double f;
long f; long fbits;
if (x < 0) { if (x < 0) {
s = 1; s = 1;
@ -226,13 +226,15 @@ pack_float(x, p, incr)
} }
else else
s = 0; s = 0;
fl = frexp(x, &e);
/* Normalize fl to be in the range [1.0, 2.0) */ f = frexp(x, &e);
if (0.5 <= fl && fl < 1.0) {
fl *= 2.0; /* Normalize f to be in the range [1.0, 2.0) */
if (0.5 <= f && f < 1.0) {
f *= 2.0;
e--; e--;
} }
else if (fl == 0.0) { else if (f == 0.0) {
e = 0; e = 0;
} }
else { else {
@ -240,41 +242,40 @@ pack_float(x, p, incr)
"frexp() result out of range"); "frexp() result out of range");
return -1; return -1;
} }
e += 127;
if (e >= 255) { if (e >= 128) {
/* XXX 255 itself is reserved for Inf/NaN */ /* XXX 128 itself is reserved for Inf/NaN */
PyErr_SetString(PyExc_OverflowError, PyErr_SetString(PyExc_OverflowError,
"float too large to pack with f format"); "float too large to pack with f format");
return -1; return -1;
} }
else if (e <= 0) { else if (e < -126) {
/* XXX Underflow -- could do better, but who cares? */ /* Gradual underflow */
fl = 0.0; f = ldexp(f, 126 + e);
e = 0; e = 0;
} }
if (fl == 0.0) {
f = 0;
}
else { else {
fl -= 1.0; /* Get rid of leading 1 */ e += 127;
fl *= 8388608.0; /* 2**23 */ f -= 1.0; /* Get rid of leading 1 */
f = (long) floor(fl + 0.5); /* Round */
} }
f *= 8388608.0; /* 2**23 */
fbits = (long) floor(f + 0.5); /* Round */
/* First byte */ /* First byte */
*p = (s<<7) | (e>>1); *p = (s<<7) | (e>>1);
p += incr; p += incr;
/* Second byte */ /* Second byte */
*p = ((e&1)<<7) | (f>>16); *p = ((e&1)<<7) | (fbits>>16);
p += incr; p += incr;
/* Third byte */ /* Third byte */
*p = (f>>8) & 0xFF; *p = (fbits>>8) & 0xFF;
p += incr; p += incr;
/* Fourth byte */ /* Fourth byte */
*p = f&0xFF; *p = fbits&0xFF;
/* Done */ /* Done */
return 0; return 0;
@ -288,7 +289,7 @@ pack_double(x, p, incr)
{ {
int s; int s;
int e; int e;
double fl; double f;
long fhi, flo; long fhi, flo;
if (x < 0) { if (x < 0) {
@ -297,13 +298,15 @@ pack_double(x, p, incr)
} }
else else
s = 0; s = 0;
fl = frexp(x, &e);
/* Normalize fl to be in the range [1.0, 2.0) */ f = frexp(x, &e);
if (0.5 <= fl && fl < 1.0) {
fl *= 2.0; /* Normalize f to be in the range [1.0, 2.0) */
if (0.5 <= f && f < 1.0) {
f *= 2.0;
e--; e--;
} }
else if (fl == 0.0) { else if (f == 0.0) {
e = 0; e = 0;
} }
else { else {
@ -311,31 +314,30 @@ pack_double(x, p, incr)
"frexp() result out of range"); "frexp() result out of range");
return -1; return -1;
} }
e += 1023;
if (e >= 2047) { if (e >= 1024) {
/* XXX 2047 itself is reserved for Inf/NaN */ /* XXX 1024 itself is reserved for Inf/NaN */
PyErr_SetString(PyExc_OverflowError, PyErr_SetString(PyExc_OverflowError,
"float too large to pack with d format"); "float too large to pack with d format");
return -1; return -1;
} }
else if (e <= 0) { else if (e < -1022) {
/* XXX Underflow -- could do better, but who cares? */ /* Gradual underflow */
fl = 0.0; f = ldexp(f, 1022 + e);
e = 0; e = 0;
} }
if (fl == 0.0) {
fhi = flo = 0;
}
else { else {
/* fhi receives the high 28 bits; flo the low 24 bits */ e += 1023;
fl -= 1.0; f -= 1.0; /* Get rid of leading 1 */
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 */
} }
/* 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 */ /* First byte */
*p = (s<<7) | (e>>4); *p = (s<<7) | (e>>4);
p += incr; p += incr;