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WIP, bignum2 unsigned subtraction

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Justin Ethier 2022-06-19 10:16:37 -04:00
parent 244041c62b
commit 53a37be833
2 changed files with 45 additions and 4 deletions
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43
runtime.c
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@ -2306,6 +2306,11 @@ object Cyc_length_unsafe(void *data, object l)
return obj_int2obj(len); return obj_int2obj(len);
} }
/******************************************************************************
** BIGNUM 2 SECTION **/
static int bignum_cmp_unsigned(object x, object y);
char *int_to_binary(char *b, int x) char *int_to_binary(char *b, int x)
{ {
unsigned int i = 0x80000000, leading_zeros = 1; unsigned int i = 0x80000000, leading_zeros = 1;
@ -3155,28 +3160,55 @@ object bignum2_plus_unsigned(void *data, bignum2_type *x, bignum2_type *y, int n
return C_bignum_simplify(result); return C_bignum_simplify(result);
} }
static int bignum_cmp_unsigned(object x, object y)
{
uint32_t xlen = C_bignum_size(x), ylen = C_bignum_size(y);
if (xlen < ylen) {
return -1;
} else if (xlen > ylen) {
return 1;
} else if (x == y) {
return 0;
} else {
uint32_t *startx = C_bignum_digits(x),
*scanx = startx + xlen,
*scany = C_bignum_digits(y) + ylen;
while (startx < scanx) {
uint32_t xdigit = (*--scanx), ydigit = (*--scany);
if (xdigit < ydigit)
return -1;
if (xdigit > ydigit)
return 1;
}
return 0;
}
}
//static //static
object bignum_minus_unsigned(void *data, object x, object y) object bignum_minus_unsigned(void *data, object x, object y)
{ {
object res; object res, tmp;
uint32_t size; uint32_t size;
uint32_t *scan_r, *end_r, *scan_y, *end_y, difference, digit; uint32_t *scan_r, *end_r, *scan_y, *end_y, difference, digit;
int borrow = 0; int borrow = 0;
switch(bignum_cmp_unsigned(x, y)) { switch(bignum_cmp_unsigned(x, y)) {
case 0: /* x = y, return 0 */ case 0: /* x = y, return 0 */
return C_fix(0); return obj_int2obj(0);
case -1: /* abs(x) < abs(y), return -(abs(y) - abs(x)) */ case -1: /* abs(x) < abs(y), return -(abs(y) - abs(x)) */
size = C_bignum_size(y); /* Maximum size of result is length of y. */ size = C_bignum_size(y); /* Maximum size of result is length of y. */
size = y; tmp = y;
y = x; y = x;
x = size; x = tmp;
break; break;
case 1: /* abs(x) > abs(y), return abs(x) - abs(y) */ case 1: /* abs(x) > abs(y), return abs(x) - abs(y) */
default: default:
size = C_bignum_size(x); /* Maximum size of result is length of x. */ size = C_bignum_size(x); /* Maximum size of result is length of x. */
break; break;
} }
res = gc_alloc_bignum2(data, size);
scan_r = C_bignum_digits(res); scan_r = C_bignum_digits(res);
end_r = scan_r + C_bignum_size(res); end_r = scan_r + C_bignum_size(res);
@ -3211,6 +3243,9 @@ object bignum_minus_unsigned(void *data, object x, object y)
return C_bignum_simplify(res); return C_bignum_simplify(res);
} }
/** END BIGNUM 2 SECTION **
******************************************************************************/
object Cyc_symbol2string(void *data, object cont, object sym) object Cyc_symbol2string(void *data, object cont, object sym)
{ {
Cyc_check_sym(data, sym); Cyc_check_sym(data, sym);

6
test-bn.scm
View file

@ -88,6 +88,12 @@ if(is_value_type(result)) {
(write row) (write row)
(newline)) (newline))
(list (list
(test-minus ;; TODO: just hangs, WTF?
(test-str2bn "1234567890123456789012345678901234567890")
(test-str2bn "1234567890"))
(test-minus
(test-str2bn "1234567890")
(test-str2bn "1234567890123456789012345678901234567890"))
(test-minus 1 1) (test-minus 1 1)
(test-minus 1 2) (test-minus 1 2)
(test-minus -1 2) (test-minus -1 2)