Re: [PATCH v2 5/6] ecc: Add powerpc64 assembly for ecc_25519_modp

Amitay Isaacs amitay@ozlabs.org writes:

--- /dev/null +++ b/powerpc64/ecc-curve25519-modp.asm @@ -0,0 +1,101 @@ +C powerpc64/ecc-25519-modp.asm +define(`RP', `r4') +define(`XP', `r5')

+define(`U0', `r6') C Overlaps unused modulo input +define(`U1', `r7') +define(`U2', `r8') +define(`U3', `r9') +define(`T0', `r10') +define(`T1', `r11') +define(`M', `r12')

+define(`UN', r3)

Comment seems misplaced, it's UN / r3 that overlaps the unused input, right?

• C void ecc_curve25519_modp (const struct ecc_modulo *p, mp_limb_t *rp, mp_limb_t *xp)
• .text

+define(`FUNC_ALIGN', `5') +PROLOGUE(_nettle_ecc_curve25519_modp)

• C First fold the limbs affecting bit 255
• ld UN, 56(XP)
• li M, 38
• mulhdu T1, M, UN
• mulld UN, M, UN
• ld U3, 24(XP)
• li T0, 0
• addc U3, UN, U3
• adde T0, T1, T0
• ld UN, 40(XP)
• mulhdu U2, M, UN
• mulld UN, M, UN
• addc U3, U3, U3
• adde T0, T0, T0
• srdi U3, U3, 1 C Undo shift, clear high bit
• C Fold the high limb again, together with RP[5]
• li T1, 19
• mulld T0, T1, T0
• ld U0, 0(XP)
• ld U1, 8(XP)
• ld T1, 16(XP)
• addc U0, T0, U0
• adde U1, UN, U1
• ld T0, 32(XP)
• adde U2, U2, T1
• addze U3, U3
• mulhdu T1, M, T0
• mulld T0, M, T0
• addc U0, T0, U0
• adde U1, T1, U1
• std U0, 0(RP)
• std U1, 8(RP)
• ld T0, 48(XP)
• mulhdu T1, M, T0
• mulld UN, M, T0
• adde U2, UN, U2
• adde U3, T1, U3
• std U2, 16(RP)
• std U3, 24(RP)
• blr

+EPILOGUE(_nettle_ecc_curve25519_modp)

Looks good. I must admit that the x86_64 version this is based on is not so easy to follow.

Regards, /Niels