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Support float and double in non-native formats.
These use the ANSI/IEEE standard, which is also used by XDR; so the _xdr module may become obsolete.
This commit is contained in:
Guido van Rossum
parent
9e3fceb5b3
commit
74679b455f
1 changed files with 365 additions and 2 deletions
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@ -35,6 +35,7 @@ PERFORMANCE OF THIS SOFTWARE.
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character strings, and unsigned numbers */
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#include "Python.h"
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#include "mymath.h"
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#include <limits.h>
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@ -200,6 +201,274 @@ get_ulong(v, p)
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}
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/* Floating point helpers */
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/* These use ANSI/IEEE Standard 754-1985 (Standard for Binary Floating
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Point Arithmetic). See the following URL:
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http://www.psc.edu/general/software/packages/ieee/ieee.html */
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/* XXX Signed zero, infinity, underflow, NaN are not handled quite right? */
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static int
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pack_float(x, p, incr)
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double x; /* The number to pack */
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char *p; /* Where to pack the high order byte */
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int incr; /* 1 for big-endian; -1 for little-endian */
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{
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int s;
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int e;
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double fl;
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long f;
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if (x < 0) {
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s = 1;
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x = -x;
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}
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else
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s = 0;
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fl = frexp(x, &e);
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/* Normalize fl to be in the range [1.0, 2.0) */
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if (0.5 <= fl && fl < 1.0) {
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fl *= 2.0;
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e--;
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}
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else if (fl == 0.0) {
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e = 0;
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}
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else {
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PyErr_SetString(PyExc_SystemError,
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"frexp() result out of range");
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return -1;
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}
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e += 127;
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if (e >= 255) {
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/* XXX 255 itself is reserved for Inf/NaN */
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PyErr_SetString(PyExc_OverflowError,
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"float too large to pack with f format");
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return -1;
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}
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else if (e <= 0) {
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/* XXX Underflow -- could do better, but who cares? */
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fl = 0.0;
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e = 0;
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}
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if (fl == 0.0) {
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f = 0;
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}
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else {
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fl -= 1.0; /* Get rid of leading 1 */
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fl *= 8388608.0; /* 2**23 */
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f = (long) floor(fl + 0.5); /* Round */
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}
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/* First byte */
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*p = (s<<7) | (e>>1);
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p += incr;
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/* Second byte */
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*p = ((e&1)<<7) | (f>>16);
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p += incr;
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/* Third byte */
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*p = (f>>8) & 0xFF;
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p += incr;
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/* Fourth byte */
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*p = f&0xFF;
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/* Done */
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return 0;
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}
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static int
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pack_double(x, p, incr)
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double x; /* The number to pack */
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char *p; /* Where to pack the high order byte */
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int incr; /* 1 for big-endian; -1 for little-endian */
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{
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int s;
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int e;
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double fl;
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long fhi, flo;
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if (x < 0) {
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s = 1;
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x = -x;
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}
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else
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s = 0;
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fl = frexp(x, &e);
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/* Normalize fl to be in the range [1.0, 2.0) */
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if (0.5 <= fl && fl < 1.0) {
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fl *= 2.0;
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e--;
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}
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else if (fl == 0.0) {
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e = 0;
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}
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else {
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PyErr_SetString(PyExc_SystemError,
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"frexp() result out of range");
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return -1;
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}
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e += 1023;
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if (e >= 2047) {
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/* XXX 2047 itself is reserved for Inf/NaN */
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PyErr_SetString(PyExc_OverflowError,
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"float too large to pack with d format");
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return -1;
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}
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else if (e <= 0) {
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/* XXX Underflow -- could do better, but who cares? */
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fl = 0.0;
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e = 0;
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}
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if (fl == 0.0) {
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fhi = flo = 0;
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}
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else {
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/* fhi receives the high 28 bits; flo the low 24 bits */
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fl -= 1.0;
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fl *= 268435456.0; /* 2**28 */
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fhi = (long) floor(fl); /* Truncate */
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fl -= (double)fhi;
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fl *= 16777216.0; /* 2**24 */
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flo = (long) floor(fl + 0.5); /* Round */
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}
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/* First byte */
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*p = (s<<7) | (e>>4);
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p += incr;
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/* Second byte */
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*p = ((e&0xF)<<4) | (fhi>>24);
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p += incr;
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/* Third byte */
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*p = (fhi>>16) & 0xFF;
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p += incr;
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/* Fourth byte */
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*p = (fhi>>8) & 0xFF;
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p += incr;
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/* Fifth byte */
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*p = fhi & 0xFF;
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p += incr;
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/* Sixth byte */
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*p = (flo>>16) & 0xFF;
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p += incr;
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/* Seventh byte */
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*p = (flo>>8) & 0xFF;
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p += incr;
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/* Eighth byte */
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*p = flo & 0xFF;
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p += incr;
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/* Done */
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return 0;
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}
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static PyObject *
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unpack_float(p, incr)
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char *p; /* Where the high order byte is */
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int incr; /* 1 for big-endian; -1 for little-endian */
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{
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int s;
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int e;
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long f;
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double x;
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/* First byte */
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s = (*p>>7) & 1;
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e = (*p & 0x7F) << 1;
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p += incr;
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/* Second byte */
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e |= (*p>>7) & 1;
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f = (*p & 0x7F) << 16;
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p += incr;
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/* Third byte */
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f |= (*p & 0xFF) << 8;
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p += incr;
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/* Fourth byte */
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f |= *p & 0xFF;
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x = (double)f / 8388608.0;
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/* XXX This sadly ignores Inf/NaN issues */
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if (e != 0)
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x = ldexp(1.0 + x, e - 127);
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if (s)
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x = -x;
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return PyFloat_FromDouble(x);
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}
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static PyObject *
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unpack_double(p, incr)
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char *p; /* Where the high order byte is */
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int incr; /* 1 for big-endian; -1 for little-endian */
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{
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int s;
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int e;
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long fhi, flo;
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double x;
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/* First byte */
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s = (*p>>7) & 1;
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e = (*p & 0x7F) << 4;
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p += incr;
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/* Second byte */
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e |= (*p>>4) & 0xF;
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fhi = (*p & 0xF) << 24;
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p += incr;
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/* Third byte */
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fhi |= (*p & 0xFF) << 16;
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p += incr;
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/* Fourth byte */
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fhi |= (*p & 0xFF) << 8;
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p += incr;
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/* Fifth byte */
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fhi |= *p & 0xFF;
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p += incr;
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/* Sixth byte */
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flo = (*p & 0xFF) << 16;
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p += incr;
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/* Seventh byte */
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flo |= (*p & 0xFF) << 8;
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p += incr;
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/* Eighth byte */
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flo |= *p & 0xFF;
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p += incr;
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x = (double)fhi + (double)flo / 16777216.0; /* 2**24 */
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x /= 268435456.0; /* 2**28 */
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/* XXX This sadly ignores Inf/NaN */
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if (e != 0)
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x = ldexp(1.0 + x, e - 1023);
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if (s)
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x = -x;
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return PyFloat_FromDouble(x);
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}
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/* The translation function for each format character is table driven */
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typedef struct _formatdef {
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@ -486,6 +755,22 @@ bu_uint(p, f)
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return PyLong_FromLong(x);
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}
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static PyObject *
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bu_float(p, f)
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const char *p;
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const formatdef *f;
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{
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return unpack_float(p, 1);
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}
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static PyObject *
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bu_double(p, f)
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const char *p;
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const formatdef *f;
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{
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return unpack_double(p, 1);
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}
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static int
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bp_int(p, v, f)
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char *p;
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@ -522,6 +807,36 @@ bp_uint(p, v, f)
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return 0;
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}
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static int
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bp_float(p, v, f)
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char *p;
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PyObject *v;
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const formatdef *f;
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{
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double x = PyFloat_AsDouble(v);
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if (x == -1 && PyErr_Occurred()) {
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PyErr_SetString(StructError,
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"required argument is not a float");
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return -1;
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}
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return pack_float(x, p, 1);
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}
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static int
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bp_double(p, v, f)
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char *p;
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PyObject *v;
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const formatdef *f;
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{
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double x = PyFloat_AsDouble(v);
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if (x == -1 && PyErr_Occurred()) {
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PyErr_SetString(StructError,
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"required argument is not a float");
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return -1;
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}
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return pack_double(x, p, 1);
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}
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static formatdef bigendian_table[] = {
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{'x', 1, 0, NULL},
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{'b', 1, 0, bu_int, bp_int},
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@ -534,7 +849,8 @@ static formatdef bigendian_table[] = {
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{'I', 4, 0, bu_uint, bp_uint},
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{'l', 4, 0, bu_int, bp_int},
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{'L', 4, 0, bu_uint, bp_uint},
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/* No float and double! */
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{'f', 4, 0, bu_float, bp_float},
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{'d', 8, 0, bu_double, bp_double},
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{0}
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};
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@ -572,6 +888,22 @@ lu_uint(p, f)
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return PyLong_FromLong(x);
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}
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static PyObject *
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lu_float(p, f)
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const char *p;
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const formatdef *f;
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{
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return unpack_float(p+3, -1);
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}
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static PyObject *
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lu_double(p, f)
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const char *p;
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const formatdef *f;
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{
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return unpack_double(p+7, -1);
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}
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static int
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lp_int(p, v, f)
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char *p;
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@ -608,6 +940,36 @@ lp_uint(p, v, f)
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return 0;
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}
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static int
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lp_float(p, v, f)
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char *p;
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PyObject *v;
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const formatdef *f;
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{
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double x = PyFloat_AsDouble(v);
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if (x == -1 && PyErr_Occurred()) {
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PyErr_SetString(StructError,
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"required argument is not a float");
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return -1;
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}
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return pack_float(x, p+3, -1);
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}
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static int
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lp_double(p, v, f)
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char *p;
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PyObject *v;
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const formatdef *f;
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{
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double x = PyFloat_AsDouble(v);
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if (x == -1 && PyErr_Occurred()) {
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PyErr_SetString(StructError,
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"required argument is not a float");
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return -1;
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}
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return pack_double(x, p+7, -1);
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}
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static formatdef lilendian_table[] = {
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{'x', 1, 0, NULL},
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{'b', 1, 0, lu_int, lp_int},
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@ -620,7 +982,8 @@ static formatdef lilendian_table[] = {
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{'I', 4, 0, lu_uint, lp_uint},
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{'l', 4, 0, lu_int, lp_int},
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{'L', 4, 0, lu_uint, lp_uint},
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/* No float and double! */
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{'f', 4, 0, lu_float, lp_float},
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{'d', 8, 0, lu_double, lp_double},
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{0}
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};
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