Use the following SSSE3 intrinsics for negation.
extern __m128i _mm_sign_epi8 (__m128i a, __m128i b);
Negate packed bytes in a if corresponding sign in b is less than zero.
Interpreting a, b, and r as arrays of signed 8-bit integers:
for (i = 0; i < 16; i++) {
if (b[i] < 0) {
r[i] = -a[i];
}
else if (b[i] == 0) {
r[i] = 0;
}
else {
r[i] = a[i];
}
}
extern __m128i _mm_sign_epi16 (__m128i a, __m128i b);
Negate packed words in a if corresponding sign in b is less than zero.
Interpreting a, b, and r as arrays of signed 16-bit integers:
for (i = 0; i < 8; i++) {
if (b[i] < 0) {
r[i] = -a[i];
}
else if (b[i] == 0) {
r[i] = 0;
}
else {
r[i] = a[i];
}
}
extern __m128i _mm_sign_epi32 (__m128i a, __m128i b);
Negate packed dwords in a if corresponding sign in b is less than zero.
Interpreting a, b, and r as arrays of signed 32-bit integers:
for (i = 0; i < 4; i++) {
if (b[i] < 0) {
r[i] = -a[i];
}
else if (b[i] == 0) {
r[i] = 0;
}
else {
r[i] = a[i];
}
}
extern __m64 _mm_sign_pi8 (__m64 a, __m64 b);
Negate packed bytes in a if corresponding sign in b is less than zero.
Interpreting a, b, and r as arrays of signed 8-bit integers:
for (i = 0; i < 16; i++) {
if (b[i] < 0) {
r[i] = -a[i];
}
else if (b[i] == 0) {
r[i] = 0;
}
else {
r[i] = a[i];
}
}
extern __m64 _mm_sign_pi16 (__m64 a, __m64 b);
Negate packed words in a if corresponding sign in b is less than zero.
Interpreting a, b, and r as arrays of signed 16-bit integers:
for (i = 0; i < 8; i++) {
if (b[i] < 0) {
r[i] = -a[i];
}
else if (b[i] == 0) {
r[i] = 0;
}
else {
r[i] = a[i];
}
}
extern __m64 _mm_sign_pi32 (__m64 a, __m64 b);
Negate packed dwords in a if corresponding sign in b is less than zero.
Interpreting a, b, and r as arrays of signed 32-bit integers:
for (i = 0; i < 2; i++) {
if (b[i] < 0) {
r[i] = -a[i];
}
else if (b[i] == 0) {
r[i] = 0;
}
else {
r[i] = a[i];
}
}