test(verify): prove the riscv64 vector families through the link-parity kernel

Assisted-by: GLM 5.3 Flash

verify/testdata/linkvec_riscv64.s

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+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "textflag.h"
+
+// The vector link-regression kernel for riscv64: the RVV load/store and
+// arithmetic families computing a checksum end to end.  bytetotal
+// strip-mines a byte buffer with VSETVLI, loads each chunk with VLE8V,
+// widens it to E64 lanes with VSEXTVF8 and reduces the chunk with
+// VREDSUMVS, so the result never depends on the hardware VLEN.  checksum
+// passes the slice to bytetotal through the ABI0 stack slots and mixes the
+// reduction with the seed through the intra-file mix call.  mix multiplies
+// by the odd golden-ratio constant and XORs the seed, the same arithmetic
+// the Go side of the regression mirrors bit for bit.
+
+// func bytetotal(buf []byte) int64
+TEXT ·bytetotal(SB), NOSPLIT, $0-32
+	MOV       buf+0(FP), X10
+	MOV       buf_len+8(FP), X12
+	MOV       $0, X13
+	BEQZ      X12, empty
+
+loop:
+	VSETVLI   X12, E64, M1, TA, MA, X11
+	VLE8V     (X10), V16
+	VSEXTVF8  V16, V9
+	VMVVI     $0, V10
+	VREDSUMVS V10, V9, V11
+	VMVXS     V11, X14
+	ADD       X14, X13, X13
+	ADD       X11, X10, X10
+	SUB       X11, X12, X12
+	BNE       X12, X0, loop
+
+empty:
+	MOV       X13, ret+24(FP)
+	RET
+
+// func mix(x, seed int64) int64
+TEXT ·mix(SB), NOSPLIT, $0-24
+	MOV x+0(FP), X10
+	MOV seed+8(FP), X11
+	MOV $0x0101010101010101, X12
+	MUL X12, X10, X10
+	XOR X11, X10, X10
+	MOV X10, ret+16(FP)
+	RET
+
+// func checksum(buf []byte, seed int64) int64
+TEXT ·checksum(SB), NOSPLIT, $40-40
+	MOV  buf+0(FP), X10
+	MOV  buf+8(FP), X11
+	MOV  buf+16(FP), X12
+	MOV  X10, 8(SP)
+	MOV  X11, 16(SP)
+	MOV  X12, 24(SP)
+	CALL ·bytetotal(SB)
+	MOV  32(SP), X10
+	MOV  seed+24(FP), X11
+	MOV  X10, 8(SP)
+	MOV  X11, 16(SP)
+	CALL ·mix(SB)
+	MOV  24(SP), X10
+	MOV  X10, ret+32(FP)
+	RET