libbb/yescrypt: code shrink

function                                             old     new   delta
static.PBKDF2_SHA256                                 219     165     -54

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/libbb/yescrypt/alg-sha256.c b/libbb/yescrypt/alg-sha256.c
index 20e8d1ee4..dc748c968 100644
--- a/libbb/yescrypt/alg-sha256.c
+++ b/libbb/yescrypt/alg-sha256.c
@@ -47,9 +47,12 @@ PBKDF2_SHA256(const uint8_t *passwd, size_t passwdlen,
 
         /* Iterate through the blocks. */
         for (i = 0; dkLen != 0; ) {
-                uint64_t U[32 / 8];
-                uint64_t T[32 / 8];
-                uint64_t j;
+                long U[32 / sizeof(long)];
+                long T[32 / sizeof(long)];
+// Do not make these ^^ uint64_t[]. Keep them long[].
+// Even though the XORing loop below is optimized out,
+// gcc is not smart enough to realize that 64-bit alignment of the stack
+// is no longer useful, and generates ~50 more bytes of code on i386...
                 uint32_t ivec;
                 size_t clen;
                 int k;
@@ -64,13 +67,15 @@ PBKDF2_SHA256(const uint8_t *passwd, size_t passwdlen,
 //does libbb need a non-vararg version with just one (buf,len)?
 
                 if (c > 1) {
+//in yescrypt, c is always 1, so this if() branch is optimized out
+                        uint64_t j;
                         /* T_i = U_1 ... */
                         memcpy(U, T, 32);
                         for (j = 2; j <= c; j++) {
                                 /* Compute U_j. */
                                 hmac_peek_hash(&Phctx, (void*)U, U, 32, NULL);
                                 /* ... xor U_j ... */
-                                for (k = 0; k < 32 / 8; k++)
+                                for (k = 0; k < 32 / sizeof(long); k++)
                                         T[k] ^= U[k];
                                 //TODO: xorbuf32_aligned_long(T, U);
                         }