static int bf_add_internal()

in GaiaXAndroidQuickJS/quickjs/gxquickjs/libbf.c [868:1010]

• 118 lines of code
• 26 McCabe index (conditional complexity)

static int bf_add_internal(bf_t *r, const bf_t *a, const bf_t *b, limb_t prec,
                           bf_flags_t flags, int b_neg)
{
    const bf_t *tmp;
    int is_sub, ret, cmp_res, a_sign, b_sign;

    a_sign = a->sign;
    b_sign = b->sign ^ b_neg;
    is_sub = a_sign ^ b_sign;
    cmp_res = bf_cmpu(a, b);
    if (cmp_res < 0) {
        tmp = a;
        a = b;
        b = tmp;
        a_sign = b_sign; /* b_sign is never used later */
    }
    /* abs(a) >= abs(b) */
    if (cmp_res == 0 && is_sub && a->expn < BF_EXP_INF) {
        /* zero result */
        bf_set_zero(r, (flags & BF_RND_MASK) == BF_RNDD);
        ret = 0;
    } else if (a->len == 0 || b->len == 0) {
        ret = 0;
        if (a->expn >= BF_EXP_INF) {
            if (a->expn == BF_EXP_NAN) {
                /* at least one operand is NaN */
                bf_set_nan(r);
            } else if (b->expn == BF_EXP_INF && is_sub) {
                /* infinities with different signs */
                bf_set_nan(r);
                ret = BF_ST_INVALID_OP;
            } else {
                bf_set_inf(r, a_sign);
            }
        } else {
            /* at least one zero and not subtract */
            bf_set(r, a);
            r->sign = a_sign;
            goto renorm;
        }
    } else {
        slimb_t d, a_offset, b_bit_offset, i, cancelled_bits;
        limb_t carry, v1, v2, u, r_len, carry1, precl, tot_len, z, sub_mask;

        r->sign = a_sign;
        r->expn = a->expn;
        d = a->expn - b->expn;
        /* must add more precision for the leading cancelled bits in
           subtraction */
        if (is_sub) {
            if (d <= 1)
                cancelled_bits = count_cancelled_bits(a, b);
            else
                cancelled_bits = 1;
        } else {
            cancelled_bits = 0;
        }
        
        /* add two extra bits for rounding */
        precl = (cancelled_bits + prec + 2 + LIMB_BITS - 1) / LIMB_BITS;
        tot_len = bf_max(a->len, b->len + (d + LIMB_BITS - 1) / LIMB_BITS);
        r_len = bf_min(precl, tot_len);
        if (bf_resize(r, r_len))
            goto fail;
        a_offset = a->len - r_len;
        b_bit_offset = (b->len - r_len) * LIMB_BITS + d;

        /* compute the bits before for the rounding */
        carry = is_sub;
        z = 0;
        sub_mask = -is_sub;
        i = r_len - tot_len;
        while (i < 0) {
            slimb_t ap, bp;
            BOOL inflag;
            
            ap = a_offset + i;
            bp = b_bit_offset + i * LIMB_BITS;
            inflag = FALSE;
            if (ap >= 0 && ap < a->len) {
                v1 = a->tab[ap];
                inflag = TRUE;
            } else {
                v1 = 0;
            }
            if (bp + LIMB_BITS > 0 && bp < (slimb_t)(b->len * LIMB_BITS)) {
                v2 = get_bits(b->tab, b->len, bp);
                inflag = TRUE;
            } else {
                v2 = 0;
            }
            if (!inflag) {
                /* outside 'a' and 'b': go directly to the next value
                   inside a or b so that the running time does not
                   depend on the exponent difference */
                i = 0;
                if (ap < 0)
                    i = bf_min(i, -a_offset);
                /* b_bit_offset + i * LIMB_BITS + LIMB_BITS >= 1
                   equivalent to 
                   i >= ceil(-b_bit_offset + 1 - LIMB_BITS) / LIMB_BITS)
                */
                if (bp + LIMB_BITS <= 0)
                    i = bf_min(i, (-b_bit_offset) >> LIMB_LOG2_BITS);
            } else {
                i++;
            }
            v2 ^= sub_mask;
            u = v1 + v2;
            carry1 = u < v1;
            u += carry;
            carry = (u < carry) | carry1;
            z |= u;
        }
        /* and the result */
        for(i = 0; i < r_len; i++) {
            v1 = get_limbz(a, a_offset + i);
            v2 = get_bits(b->tab, b->len, b_bit_offset + i * LIMB_BITS);
            v2 ^= sub_mask;
            u = v1 + v2;
            carry1 = u < v1;
            u += carry;
            carry = (u < carry) | carry1;
            r->tab[i] = u;
        }
        /* set the extra bits for the rounding */
        r->tab[0] |= (z != 0);

        /* carry is only possible in add case */
        if (!is_sub && carry) {
            if (bf_resize(r, r_len + 1))
                goto fail;
            r->tab[r_len] = 1;
            r->expn += LIMB_BITS;
        }
    renorm:
        ret = bf_normalize_and_round(r, prec, flags);
    }
    return ret;
 fail:
    bf_set_nan(r);
    return BF_ST_MEM_ERROR;
}