Had you seen results from an Athlon previously? Is it possible that compiler switches are somehow geared toward Intel chips?

I've found in the past WavPack had some strange behaviour from this point of view. I used to repeat my test on a PIV, a PIII and a Sempron. When compared to other encoders, WavPack usually showed bad behaviour on the PIII. I think I still should have some tables around...

Anyway, here's some results on an Athlon64 3500+:

4.40.0 4.41.0b Enhancement

f 121,9x 152,3x 132,1x 163,3x 8,4% 7,2%

fx1 70,0x 152,3x 77,0x 160,3x 10,0% 5,3%

fx2 50,5x 150,6x 57,5x 159,8x 13,9% 6,1%

fx3 30,7x 149,7x 35,7x 159,3x 16,3% 6,4%

fx4 13,0x 149,7x 15,1x 158,8x 16,2% 6,1%

fx5 10,5x 147,9x 12,2x 158,3x 16,2% 7,0%

fx6 9,0x 146,7x 10,4x 156,9x 15,6% 7,0%

100,8x 131,1x 111,0x 135,6x 10,1% 3,4%

x1 51,8x 129,5x 60,7x 134,9x 17,2% 4,2%

x2 33,8x 129,2x 41,1x 131,5x 21,6% 1,8%

x3 18,3x 127,9x 23,0x 131,1x 25,7% 2,5%

x4 4,8x 127,6x 5,8x 130,8x 20,8% 2,5%

x5 3,4x 126,7x 4,0x 130,5x 17,6% 3,0%

x6 1,7x 124,8x 2,0x 129,5x 17,6% 3,8%

h 74,5x 100,8x 83,4x 105,5x 11,9% 4,7%

hx1 36,5x 100,4x 43,8x 104,3x 20,0% 3,9%

hx2 21,7x 100,1x 27,0x 102,4x 24,4% 2,3%

hx3 10,9x 100,1x 13,8x 101,4x 26,6% 1,3%

hx4 2,9x 99,7x 3,5x 101,0x 20,7% 1,3%

hx5 2,2x 99,3x 2,7x 100,8x 22,7% 1,5%

hx6 1,5x 98,7x 1,8x 100,1x 20,0% 1,4%

hh 60,5x 80,6x 67,7x 81,8x 11,9% 1,5%

hhx1 26,8x 80,3x 33,5x 81,6x 25,0% 1,6%

hhx2 15,3x 79,9x 19,5x 81,5x 27,5% 2,0%

hhx3 7,4x 79,6x 9,6x 81,3x 29,7% 2,1%

While on the decoding side the improvements are not as dramatic as they are on the tests on the Intel chips above, nevertheless the encoding speed improvements seems very good also on this AMD chip test.