Some small performance improvements on 32-bit architectures.

[BearSSL] / src / int / i31_mulacc.c

diff --git a/src/int/i31_mulacc.c b/src/int/i31_mulacc.c
index 024d095..7410e54 100644 (file)
--- a/src/int/i31_mulacc.c
+++ b/src/int/i31_mulacc.c
@@ -45,7 +45,20 @@ br_i31_mulacc(uint32_t *d, const uint32_t *a, const uint32_t *b)
        for (u = 0; u < blen; u ++) {
                uint32_t f;
                size_t v;
+
+               /*
+                * Carry always fits on 31 bits; we want to keep it in a
+                * 32-bit register on 32-bit architectures (on a 64-bit
+                * architecture, cast down from 64 to 32 bits means
+                * clearing the high bits, which is not free; on a 32-bit
+                * architecture, the same operation really means ignoring
+                * the top register, which has negative or zero cost).
+                */
+#if BR_64
                uint64_t cc;
+#else
+               uint32_t cc;
+#endif
 
                f = b[1 + u];
                cc = 0;