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[libc] Add ffs(), ffsl(), and ffsll() 

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown 2015-03-15 19:28:05 +00:00
parent 57bab4e1d3
commit 79697c75ee
4 changed files with 233 additions and 6 deletions
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46
src/arch/i386/include/bits/strings.h
View File

@ -3,6 +3,50 @@
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/**
* Find first (i.e. least significant) set bit
*
* @v value Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
static inline __attribute__ (( always_inline )) int __ffsl ( long value ) {
long lsb_minus_one;
/* If the input value is zero, the BSF instruction returns
* ZF=0 and leaves an undefined value in the output register.
* Perform this check in C rather than asm so that it can be
* omitted in cases where the compiler is able to prove that
* the input is non-zero.
*/
if ( value ) {
__asm__ ( "bsfl %1, %0"
: "=r" ( lsb_minus_one )
: "rm" ( value ) );
return ( lsb_minus_one + 1 );
} else {
return 0;
}
}
/**
* Find first (i.e. least significant) set bit
*
* @v value Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
static inline __attribute__ (( always_inline )) int __ffsll ( long long value ){
unsigned long high = ( value >> 32 );
unsigned long low = ( value >> 0 );
if ( low ) {
return ( __ffsl ( low ) );
} else if ( high ) {
return ( 32 + __ffsl ( high ) );
} else {
return 0;
}
}
/**
* Find last (i.e. most significant) set bit
*
@ -13,7 +57,7 @@ static inline __attribute__ (( always_inline )) int __flsl ( long value ) {
long msb_minus_one;
/* If the input value is zero, the BSR instruction returns
* ZF=1 and leaves an undefined value in the output register.
* ZF=0 and leaves an undefined value in the output register.
* Perform this check in C rather than asm so that it can be
* omitted in cases where the compiler is able to prove that
* the input is non-zero.

38
src/arch/x86_64/include/bits/strings.h
View File

@ -3,6 +3,42 @@
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/**
* Find first (i.e. least significant) set bit
*
* @v value Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
static inline __attribute__ (( always_inline )) int __ffsll ( long long value ){
long long lsb_minus_one;
/* If the input value is zero, the BSF instruction returns
* ZF=0 and leaves an undefined value in the output register.
* Perform this check in C rather than asm so that it can be
* omitted in cases where the compiler is able to prove that
* the input is non-zero.
*/
if ( value ) {
__asm__ ( "bsfq %1, %0"
: "=r" ( lsb_minus_one )
: "rm" ( value ) );
return ( lsb_minus_one + 1 );
} else {
return 0;
}
}
/**
* Find first (i.e. least significant) set bit
*
* @v value Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
static inline __attribute__ (( always_inline )) int __ffsl ( long value ) {
return __ffsll ( value );
}
/**
* Find last (i.e. most significant) set bit
*
@ -13,7 +49,7 @@ static inline __attribute__ (( always_inline )) int __flsll ( long long value ){
long long msb_minus_one;
/* If the input value is zero, the BSR instruction returns
* ZF=1 and leaves an undefined value in the output register.
* ZF=0 and leaves an undefined value in the output register.
* Perform this check in C rather than asm so that it can be
* omitted in cases where the compiler is able to prove that
* the input is non-zero.

81
src/include/strings.h
View File

@ -12,6 +12,54 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#include <string.h>
#include <bits/strings.h>
/**
* Find first (i.e. least significant) set bit
*
* @v x Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
static inline __attribute__ (( always_inline )) int
__constant_ffsll ( unsigned long long x ) {
int r = 0;
if ( ! ( x & 0x00000000ffffffffULL ) ) {
x >>= 32;
r += 32;
}
if ( ! ( x & 0x0000ffffUL ) ) {
x >>= 16;
r += 16;
}
if ( ! ( x & 0x00ff ) ) {
x >>= 8;
r += 8;
}
if ( ! ( x & 0x0f ) ) {
x >>= 4;
r += 4;
}
if ( ! ( x & 0x3 ) ) {
x >>= 2;
r += 2;
}
if ( ! ( x & 0x1 ) ) {
x >>= 1;
r += 1;
}
return ( x ? ( r + 1 ) : 0 );
}
/**
* Find first (i.e. least significant) set bit
*
* @v x Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
static inline __attribute__ (( always_inline )) int
__constant_ffsl ( unsigned long x ) {
return __constant_ffsll ( x );
}
/**
* Find last (i.e. most significant) set bit
*
@ -46,10 +94,7 @@ __constant_flsll ( unsigned long long x ) {
x >>= 1;
r += 1;
}
if ( x & 0x1 ) {
r += 1;
}
return r;
return ( x ? ( r + 1 ) : 0 );
}
/**
@ -63,9 +108,37 @@ __constant_flsl ( unsigned long x ) {
return __constant_flsll ( x );
}
int __ffsll ( long long x );
int __ffsl ( long x );
int __flsll ( long long x );
int __flsl ( long x );
/**
* Find first (i.e. least significant) set bit
*
* @v x Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
#define ffsll( x ) \
( __builtin_constant_p ( x ) ? __constant_ffsll ( x ) : __ffsll ( x ) )
/**
* Find first (i.e. least significant) set bit
*
* @v x Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
#define ffsl( x ) \
( __builtin_constant_p ( x ) ? __constant_ffsl ( x ) : __ffsl ( x ) )
/**
* Find first (i.e. least significant) set bit
*
* @v x Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
#define ffs( x ) ffsl ( x )
/**
* Find last (i.e. most significant) set bit
*

74
src/tests/math_test.c
View File

@ -38,6 +38,26 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#include <ipxe/test.h>
#include <ipxe/isqrt.h>
/**
* Force a call to the non-constant implementation of ffsl()
*
* @v value Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
__attribute__ (( noinline )) int ffsl_var ( long value ) {
return ffsl ( value );
}
/**
* Force a call to the non-constant implementation of ffsll()
*
* @v value Value
* @ret lsb Least significant bit set in value (LSB=1), or zero
*/
__attribute__ (( noinline )) int ffsll_var ( long long value ) {
return ffsll ( value );
}
/**
* Force a call to the non-constant implementation of flsl()
*
@ -176,6 +196,44 @@ __attribute__ (( noinline )) int64_t s64mod_var ( int64_t dividend,
return check_divmod ( dividend, divisor, % );
}
/**
* Report a ffsl() test result
*
* @v value Value
* @v lsb Expected LSB
* @v file Test code file
* @v line Test code line
*/
static inline __attribute__ (( always_inline )) void
ffsl_okx ( long value, int lsb, const char *file, unsigned int line ) {
/* Verify as a constant (requires to be inlined) */
okx ( ffsl ( value ) == lsb, file, line );
/* Verify as a non-constant */
okx ( ffsl_var ( value ) == lsb, file, line );
}
#define ffsl_ok( value, lsb ) ffsl_okx ( value, lsb, __FILE__, __LINE__ )
/**
* Report a ffsll() test result
*
* @v value Value
* @v lsb Expected LSB
* @v file Test code file
* @v line Test code line
*/
static inline __attribute__ (( always_inline )) void
ffsll_okx ( long long value, int lsb, const char *file, unsigned int line ) {
/* Verify as a constant (requires to be inlined) */
okx ( ffsll ( value ) == lsb, file, line );
/* Verify as a non-constant */
okx ( ffsll_var ( value ) == lsb, file, line );
}
#define ffsll_ok( value, lsb ) ffsll_okx ( value, lsb, __FILE__, __LINE__ )
/**
* Report a flsl() test result
*
@ -274,6 +332,22 @@ static void s64divmod_okx ( int64_t dividend, int64_t divisor,
*/
static void math_test_exec ( void ) {
/* Test ffsl() */
ffsl_ok ( 0, 0 );
ffsl_ok ( 1, 1 );
ffsl_ok ( 255, 1 );
ffsl_ok ( 256, 9 );
ffsl_ok ( 257, 1 );
ffsl_ok ( 0x54850596, 2 );
ffsl_ok ( 0x80000000, 32 );
/* Test ffsll() */
ffsll_ok ( 0, 0 );
ffsll_ok ( 1, 1 );
ffsll_ok ( 0x6d63623330ULL, 5 );
ffsll_ok ( 0x80000000UL, 32 );
ffsll_ok ( 0x8000000000000000ULL, 64 );
/* Test flsl() */
flsl_ok ( 0, 0 );
flsl_ok ( 1, 1 );