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.\" Copyright 2024 Andrew V.Kosteltsev (kx@radix-linux.su)
.\"
.\"
.TH circular\-shifts 3 "December 27, 2024" "libmpu" "LibMPU Programmer's Manual"
.SH NAME
\fBirol\fP, \fBiror\fP, \fBircl\fP, \fBircr\fP \- сyclic shift operations by one bit
.SH SYNOPSIS
.nf
.B #include <libmpu.h>
.PP
.BI "void irol( mpu_int *" c ", mpu_int *" a ", int " nb " );
.BI "void iror( mpu_int *" c ", mpu_int *" a ", int " nb " );
.BI "void ircl( mpu_int *" c ", mpu_int *" a ", int " nb " );
.BI "void ircr( mpu_int *" c ", mpu_int *" a ", int " nb " );
.fi
.SH DESCRIPTION
For cyclic shift operations by one bit, the input operand is a variable of size \fBnb\fP
bytes located at address \fBa\fP, the result is placed in a variable of the same size located
at address \fBc\fP. The spaces occupied by the input and output variables may overlap partially
or completely, which does not affect the correctness of the result. The content of the variable
located at address \fBa\fP will remain unchanged after the operation if the space occupied by
it does not overlap with the space occupied by variable \fBc\fP.
.PP
When performing cyclic shift operations, the carry flag \fBC\fP always contains the value of the
last pushed outward bit. The following types of cyclic shift operations are available:
.PP
.RS 3
ROL \- cyclic shift to the left by one bit.
.RE
.RS 3
ROR \- cyclic shift to the right by one bit.
.RE
.RS 3
RCL \- cyclic shift to the left by one bit involving the carry flag.
.RE
.RS 3
RCR \- cyclic shift to the right by one bit involving the carry flag.
.RE
.PP
The following tables illustrate the execution of \fBirol\fP, \fBiror\fP operations.
.nf
.sp
┌────────────────┬───┬───────────────────┬────────────┐
│ ROL(<<): │ C │ operand value │ filling │
├────────────────┼───┼───────────────────┼────────────┤
│ before │ │ 10110111 │ sign(1) │
├────────────────┼───┼───────────────────┼────────────┤
│ after │ 1 │ 01101111 │ │
└────────────────┴───┴───────────────────┴────────────┘
┌────────────────┬────────────┬───────────────────┬───┐
│ ROR(>>): │ filling │ operand value │ C │
├────────────────┼────────────┼───────────────────┼───┤
│ before │ low bit(1) │ 10110111 │ │
├────────────────┼────────────┼───────────────────┼───┤
│ after │ │ 11011011 │ 1 │
└────────────────┴────────────┴───────────────────┴───┘
.fi
.sp
The \fBirol\fP and \fBiror\fP operations (similar to the shift commands \fBisal\fP, \fBisar\fP,
\fBishl\fP, \fBishr\fP) act on the overflow flag \fBO\fP to control the sign change of the operand.
The parity \fBP\fP, sign \fBS\fP, and zero \fBZ\fP flags are also set. The carry flag from the
lowest tetrad \fBA\fP is not defined and is simply reset to 0.
.PP
In \fBircl\fP and \fBircr\fP operations, the carry flag \fBC\fP is involved in the shift.
The bit to be shifted out of the operand is written to the carry flag \fBC\fP after the
previous \fBC\fP value enters the vacant position.
.nf
.sp
┌────────────────┬───┬───────────────────┬────────────┐
│ RCL(<<): │ C │ operand value │ filling │
├────────────────┼───┼───────────────────┼────────────┤
│ before │ 0 │ 10110111 │ C(0) │
├────────────────┼───┼───────────────────┼────────────┤
│ after │ 1 │ 01101110 │ │
└────────────────┴───┴───────────────────┴────────────┘
┌────────────────┬────────────┬───────────────────┬───┐
│ RCR(>>): │ filling │ operand value │ C │
├────────────────┼────────────┼───────────────────┼───┤
│ before │ C(0) │ 10110111 │ 0 │
├────────────────┼────────────┼───────────────────┼───┤
│ after │ │ 01011011 │ 1 │
└────────────────┴────────────┴───────────────────┴───┘
.fi
.sp
The \fBircl\fP, \fBircr\fP operations affect the carry \fBC\fP and overflow \fBO\fP flags
in the same way as all previous operations. The carry flag from the lowest tetrad \fBA\fP
is not defined and is simply reset to 0.
.PP
The setting of parity \fBP\fP and zero \fBZ\fP flags by \fBircl\fP, \fBircr\fP operations
is somewhat different from the previous types of operations. This also applies to the sign
flag \fBS\fP. Since \fBircl\fP, \fBircr\fP operations can be used to shift several words
together with other shift commands and, as a rule, complete such compound operations,
it would be desirable, after their completion, to have the state of the flags \fBP\fP
and \fBZ\fP corresponding, not only to the last shifted word, but to the whole shifted
combination of words.
.PP
For this purpose, the \fBircr\fP operation sets its flags (\fBP\fP, \fBS\fP), while the \fBircl\fP
operation does not define its flags (\fBP\fP, \fBS\fP) and does not change their previous values.
The zero flag \fBZ\fP by both operations (\fBircl\fP, \fBircr\fP) is set by \fBLogical AND\fP
with the previous value of the \fBZ\fP flag, i.e.:
.nf
.sp
┌────────────────┬────────────────┬────────────────┐
│ │ Z value, │ │
│ Previous │ obtained │ Resulting │
│ Z value │ as a result of │ Z value │
│ │ operation │ │
├────────────────┼────────────────┼────────────────┤
│ 1 │ 0 │ 0 │
├────────────────┼────────────────┼────────────────┤
│ 1 │ 1 │ 1 │
├────────────────┼────────────────┼────────────────┤
│ 0 │ 0 │ 0 │
├────────────────┼────────────────┼────────────────┤
│ 0 │ 1 │ 0 │
└────────────────┴────────────────┴────────────────┘
.fi
.sp
Thus, if all words involved in the combination of shifts, gave zero result, then the flag \fBZ\fP
will remain in the value of \fBTRUE\fP, otherwise, if at least one word gave a non\-zero result,
the flag \fBZ\fP will remain in the state of \fBFALSE\fP.
.SS Examples of operations:
\fBShift a pair of words to the right\fP:
.PP
\fBisar\fP(11111101), \fBircr\fP(10011010); after \fBisar\fP result = 11111110,
\fBC\fP=1, \fBO\fP=0, \fBP\fP=1, \fBZ\fP=0; after \fBircr\fP result = 11001101,
\fBC\fP=0, \fBO\fP=0, \fBP\fP=0, \fBZ\fP=0. Total result: 1111111011001101.
The state of flags after \fBircr\fP operation is guaranteed to belong to
the whole combination of two words (8 bits each).
.sp
\fBShift a pair of words to the left\fP:
.PP
\fBircl\fP(00111000), \fBisal\fP(10111111); after \fBisal\fP result = 01111110,
\fBC\fP=1, \fBO\fP=1, \fBP\fP=1, \fBZ\fP=0; after \fBircl\fP result = 01110001,
\fBC\fP=0, \fBO\fP=0, \fBP\fP=1, \fBZ\fP=0. Total result: 0111000101111110.
The state of the flags after the \fBisal\fP operation is guaranteed to
belong to the whole combination of two words (of size 8 bits each).
Note that flag \fBP\fP is set by operation \fBisal\fP and not changed
by operation \fBircl\fP, flag \fBZ\fP is obtained by \fBAND\fP between
\fBZ\fP from \fBisal\fP and \fBZ\fP from \fBircl\fP.
.sp
.SH EXAMPLES
.nf
.sp
#include <libmpu.h>
#include <stdio.h>
int main( void )
{
int rc = 0;
__mpu_init();
__mpu_extra_warnings = 1;
{
mpu_int8_t c, d, a, b;
mpu_int16_t z;
mpu_int *pz = NULL;
__mpu_char8_t s[32];
pz = (mpu_int *)&z;
#if ( MPU_BYTE_ORDER_BIG_ENDIAN == 1 )
++pz;
#endif
iatoi( b, "0b10111111", NB_I8 ); /* low part */
iatoi( a, "0b00111000", NB_I8 ); /* high part */
__mpu_clc(); /* clear Carry Flag */
isal( d, b, NB_I8 );
ircl( c, a, NB_I8 );
icpy( pz, d, NB_I8, NB_I8 ); /* low part of Z */
#if ( MPU_BYTE_ORDER_BIG_ENDIAN == 1 )
--pz;
#else
++pz;
#endif
icpy( pz, c, NB_I8, NB_I8 ); /* high part of Z */
iitoa( s, z, RADIX_BIN, UPPERCASE, NB_I16 ); /* convert Z value to ASCII string S */
printf( "z = %s;\\n", s ); /* z = 0B0111000101111110; */
printf( "carry = %d;\\n", __mpu_gtc() ); /* Carry Flag */
printf( "overflow = %d;\\n", __mpu_gto() ); /* Overflow Flag */
}
__mpu_free_context();
return( rc );
}
.fi
.SH SEE ALSO
.BR iadd(3),
.BR isub(3),
.BR iadc(3),
.BR isbb(3),
.BR ishl(3),
.BR ishr(3),
.BR isal(3),
.BR isar(3),
.BR ishln(3),
.BR ishrn(3),
.BR isaln(3),
.BR isarn(3),
.BR iroln(3),
.BR irorn(3),
.BR ircln(3),
.BR ircrn(3),
.BR ineg(3),
.BR inot(3),
.BR iand(3),
.BR itest(3),
.BR icmp(3),
.BR ior(3),
.BR ixor(3),
.BR iinc(3),
.BR idec(3),
.BR ixchg(3),
.BR icpy(3),
.BR icvt(3),
.BR imul(3),
.BR ismul(3),
.BR idiv(3),
.BR isdiv(3),
.BR iatoi(3),
.BR iatoui(3),
.BR iitoa(3),
.BR iuitoa(3).
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