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////////////////////////////////////////////////////////////////////////////
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////////////////////////////////////////////////////////////////////////////
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//
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//
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// Filename: twoc.cpp
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// Filename: twoc.cpp
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//
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//
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// Project: A Doubletime Pipelined FFT
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// Project: Zip CPU -- a small, lightweight, RISC CPU soft core
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//
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//
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// Purpose: Some various two's complement related C++ helper routines.
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// Purpose: Some various two's complement related C++ helper routines.
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// Specifically, these help extract signed numbers from
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// Specifically, these help extract signed numbers from
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// packed bitfields, while guaranteeing that the upper bits
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// packed bitfields, while guaranteeing that the upper bits
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// are properly sign extended (or not) as desired.
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// are properly sign extended (or not) as desired.
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// License: GPL, v3, as defined and found on www.gnu.org,
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// License: GPL, v3, as defined and found on www.gnu.org,
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// http://www.gnu.org/licenses/gpl.html
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// http://www.gnu.org/licenses/gpl.html
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//
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//
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//
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//
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///////////////////////////////////////////////////////////////////////////
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///////////////////////////////////////////////////////////////////////////
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#include <stdio.h>
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#include <assert.h>
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#include "twoc.h"
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#include "twoc.h"
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long sbits(const long val, const int bits) {
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long sbits(const long val, const int bits) {
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long r;
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long r;
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if (r & (1l << (bits-1)))
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if (r & (1l << (bits-1)))
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r |= (-1l << bits);
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r |= (-1l << bits);
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return r;
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return r;
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}
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}
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bool sfits(const long val, const int bits) {
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long alt = sbits(val, bits);
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return (sbits(val, bits) == bits);
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}
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unsigned long ubits(const long val, const int bits) {
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unsigned long ubits(const long val, const int bits) {
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unsigned long r = val & ((1l<<bits)-1);
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unsigned long r = val & ((1l<<bits)-1);
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return r;
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return r;
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}
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}
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unsigned long rndbits(const long val, const int bits_in, const int bits_out) {
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long s = sbits(val, bits_in); // Signed input value
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long t = s; // Truncated input value
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long r; // Result
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// printf("RNDBITS(%08lx, %d, %d)\n", val, bits_in, bits_out);
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// printf("S = %lx\n", s);
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// printf("T = %lx\n", t);
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// assert(bits_in > bits_out);
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if (bits_in == bits_out)
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r = s;
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else if (bits_in-1 == bits_out) {
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t = sbits(val>>1, bits_out);
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// printf("TEST! S = %ld, T = %ld\n", s, t);
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if (3 == (s&3))
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t = t+1;
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r = t;
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} else {
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// A. 0XXXX.0xxxxx -> 0XXXX
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// B. 0XXX0.100000 -> 0XXX0;
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// C. 0XXX1.100000 -> 0XXX1+1;
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// D. 0XXXX.1zzzzz -> 0XXXX+1;
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// E. 1XXXX.0xxxxx -> 1XXXX
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// F. 1XXX0.100000 -> ??? XXX0;
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// G. 1XXX1.100000 -> ??? XXX1+1;
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// H. 1XXXX.1zzzzz -> 1XXXX+1;
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t = sbits(val>>(bits_in-bits_out), bits_out); // Truncated value
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if (0 == ((s >> (bits_in-bits_out-1))&1)) {
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// printf("A\n");
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r = t;
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} else if (0 != (s & ((1<<(bits_in-bits_out-1))-1))) {
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// printf("D\n");
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r = t+1;
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} else if (t&1) {
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// printf("C\n");
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r = t+1;
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} else { // 3 ..?11
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// printf("B\n");
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r = t;
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}
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} return r;
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}
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No newline at end of file
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No newline at end of file
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