+/*
+ * mask must be 0xFFFFFFFF or 0x00000000.
+ *
+ * if (mask) {
+ * uint32_t tmp = *a;
+ *
+ * *a = *b;
+ * *b = tmp;
+ * }
+ */
+static ossl_inline void constant_time_cond_swap_32(uint32_t mask, uint32_t *a,
+ uint32_t *b)
+{
+ uint32_t xor = *a ^ *b;
+
+ xor &= mask;
+ *a ^= xor;
+ *b ^= xor;
+}
+
+/*
+ * mask must be 0xFFFFFFFF or 0x00000000.
+ *
+ * if (mask) {
+ * uint64_t tmp = *a;
+ *
+ * *a = *b;
+ * *b = tmp;
+ * }
+ */
+static ossl_inline void constant_time_cond_swap_64(uint64_t mask, uint64_t *a,
+ uint64_t *b)
+{
+ uint64_t xor = *a ^ *b;
+
+ xor &= mask;
+ *a ^= xor;
+ *b ^= xor;
+}
+
+/*
+ * table is a two dimensional array of bytes. Each row has rowsize elements.
+ * Copies row number idx into out. rowsize and numrows are not considered
+ * private.
+ */
+static ossl_inline void constant_time_lookup(void *out,
+ const void *table,
+ size_t rowsize,
+ size_t numrows,
+ size_t idx)
+{
+ size_t i, j;
+ const unsigned char *tablec = (const unsigned char *)table;
+ unsigned char *outc = (unsigned char *)out;
+ unsigned char mask;
+
+ memset(out, 0, rowsize);
+
+ /* Note idx may underflow - but that is well defined */
+ for (i = 0; i < numrows; i++, idx--) {
+ mask = (unsigned char)constant_time_is_zero_s(idx);
+ for (j = 0; j < rowsize; j++)
+ *(outc + j) |= constant_time_select_8(mask, *(tablec++), 0);
+ }
+}
+