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Implemented LONGPROD, in a slightly long-winded way

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Neil Brown 2009-01-26 17:57:45 +00:00
parent df66042a99
commit 4a12999989
1 changed files with 40 additions and 5 deletions
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45
support/tock_intrinsics_arith.h
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@ -43,6 +43,46 @@ static inline INT occam_LONGDIFF (INT left, INT right, INT borrow_in, INT* resul
}
}
static inline INT occam_LONGPROD (INT, INT, INT, INT*, const char *) occam_unused;
static inline INT occam_LONGPROD (INT left, INT right, INT carry_in, INT* result1, const char *pos) {
const UINT leftu = occam_unsign(left);
const UINT rightu = occam_unsign(right);
const UINT carryu = occam_unsign(carry_in);
#define HI_HALF(x) (x >> (CHAR_BIT*sizeof(INT)/2))
#define LO_HALF(x) (x & ((1<<(CHAR_BIT*sizeof(INT)/2))-1))
#define MAKE_HI(x) (x << (CHAR_BIT*sizeof(INT)/2))
const UINT leftu_hi = HI_HALF(leftu);
const UINT rightu_hi = HI_HALF(rightu);
const UINT leftu_lo = LO_HALF(leftu);
const UINT rightu_lo = LO_HALF(rightu);
UINT prod_lo = leftu_lo * rightu_lo;
UINT prod_hi = leftu_hi * rightu_hi;
const UINT prod_med0 = leftu_lo * rightu_hi;
const UINT prod_med1 = leftu_hi * rightu_lo;
//E.g.s given for 8-bit, L=15,M=255:
//prod_hi has max value 225 (L*L)
//HI_HALF(prod_med0|1) has max value 14 (L*L)/(L+1)
//So no overflow possible here:
prod_hi += HI_HALF(prod_med0) + HI_HALF(prod_med1);
//prod_hi cannot overflow from these carries,
//As mathematically, (M*M)+M < ((M+1)*(M+1)) - 1
prod_hi += (__MAX(UINT) - prod_lo >= MAKE_HI(LO_HALF(prod_med0))) ? 0 : 1;
prod_lo += MAKE_HI(LO_HALF(prod_med0));
prod_hi += (__MAX(UINT) - prod_lo >= MAKE_HI(LO_HALF(prod_med1))) ? 0 : 1;
prod_lo += MAKE_HI(LO_HALF(prod_med1));
prod_hi += (__MAX(UINT) - prod_lo >= carryu) ? 0 : 1;
prod_lo += carryu;
*result1 = occam_sign(prod_lo);
return prod_hi;
#undef HI_HALF
#undef LO_HALF
#undef MAKE_HI
}
static inline INT occam_LONGSUB (INT, INT, INT, const char *) occam_unused;
static inline INT occam_LONGSUB (INT left, INT right, INT borrow_in, const char *pos) {
@ -106,11 +146,6 @@ static inline INT occam_NORMALISE (INT hi_in, INT lo_in, INT* result1, INT* resu
//TODO implement, and move into the correct order above:
///////////////////
static inline INT occam_LONGPROD (INT, INT, INT, INT*, const char *) occam_unused;
static inline INT occam_LONGPROD (INT left, INT right, INT carry_in, INT* result1, const char *pos) {
return 0;
}
static inline INT occam_LONGDIV (INT, INT, INT, INT*, const char *) occam_unused;
static inline INT occam_LONGDIV (INT dividend_hi, INT dividend_lo, INT divisor, INT* result1, const char *pos) {
return 0;