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// license:BSD-3-Clause
// copyright-holders:Tyler J. Stachecki,Ryan Holtz
inline rsp_vec_t vec_vsub(rsp_vec_t vs, rsp_vec_t vt, rsp_vec_t carry, rsp_vec_t *acc_lo)
{
// acc_lo uses saturated arithmetic.
rsp_vec_t unsat_diff = _mm_sub_epi16(vt, carry);
rsp_vec_t sat_diff = _mm_subs_epi16(vt, carry);
*acc_lo = _mm_sub_epi16(vs, unsat_diff);
rsp_vec_t vd = _mm_subs_epi16(vs, sat_diff);
// VD is the signed diff of the two sources and the carry. Since we
// have to saturate the diff of all three, we have to be clever.
rsp_vec_t overflow = _mm_cmpgt_epi16(sat_diff, unsat_diff);
return _mm_adds_epi16(vd, overflow);
}
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