From a47e8bba76c3b1826d62c000b707b285e70e1e78 Mon Sep 17 00:00:00 2001 From: simon Date: Wed, 23 Apr 2003 15:25:45 +0000 Subject: [PATCH] Force gcc to use x86's built-in 64/32->32,32 division instruction rather than swanning off to a helper function. This seems to make woefully little actual performance difference, which annoys me, but it's a just-about-detectable improvement so I'll leave it in. git-svn-id: svn://svn.tartarus.org/sgt/putty@3136 cda61777-01e9-0310-a592-d414129be87e --- sshbn.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/sshbn.c b/sshbn.c index a51c3a51..37422271 100644 --- a/sshbn.c +++ b/sshbn.c @@ -15,6 +15,10 @@ typedef unsigned long long BignumDblInt; #define BIGNUM_TOP_BIT 0x80000000UL #define BIGNUM_INT_BITS 32 #define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2) +#define DIVMOD_WORD(q, r, hi, lo, w) \ + __asm__("div %2" : \ + "=d" (r), "=a" (q) : \ + "r" (w), "d" (hi), "a" (lo)) #else typedef unsigned short BignumInt; typedef unsigned long BignumDblInt; @@ -22,6 +26,11 @@ typedef unsigned long BignumDblInt; #define BIGNUM_TOP_BIT 0x8000U #define BIGNUM_INT_BITS 16 #define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2) +#define DIVMOD_WORD(q, r, hi, lo, w) do { \ + BignumDblInt n = (((BignumDblInt)hi) << BIGNUM_INT_BITS) | lo; \ + q = n / w; \ + r = n % w; \ +} while (0) #endif #define BIGNUM_INT_BYTES (BIGNUM_INT_BITS / 8) @@ -175,13 +184,11 @@ static void internal_mod(BignumInt *a, int alen, ai1 = a[i + 1]; /* Find q = h:a[i] / m0 */ - t = ((BignumDblInt) h << BIGNUM_INT_BITS) + a[i]; - q = t / m0; - r = t % m0; + DIVMOD_WORD(q, r, h, a[i], m0); /* Refine our estimate of q by looking at h:a[i]:a[i+1] / m0:m1 */ - t = (BignumDblInt) m1 * (BignumDblInt) q; + t = MUL_WORD(m1, q); if (t > ((BignumDblInt) r << BIGNUM_INT_BITS) + ai1) { q--; t -= m1; @@ -193,7 +200,7 @@ static void internal_mod(BignumInt *a, int alen, /* Subtract q * m from a[i...] */ c = 0; for (k = mlen - 1; k >= 0; k--) { - t = (BignumDblInt) q * (BignumDblInt) m[k]; + t = MUL_WORD(q, m[k]); t += c; c = t >> BIGNUM_INT_BITS; if ((BignumInt) t > a[i + k]) -- 2.11.0