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@@ -23,7 +23,7 @@
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// + R11 src_base
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// + R12 src_len
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// + R13 src_base + src_len
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-// - R14 unused
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+// - R14 used by doCopy
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// - R15 used by doCopy
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//
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// The registers R8-R13 (marked with a "+") are set at the start of the
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@@ -299,10 +299,37 @@ doCopy:
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// forwardCopy(dst[d:d+length], dst[d-offset:]); d += length
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//
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// Set:
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+ // - R14 = len(dst)-d
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// - R15 = &dst[d-offset]
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+ MOVQ R10, R14
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+ SUBQ DI, R14
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MOVQ DI, R15
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SUBQ DX, R15
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+ // !!! Try a faster technique for short (16 or fewer bytes) forward copies.
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+ //
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+ // First, try using two 8-byte load/stores, similar to the doLit technique
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+ // above. Even if dst[d:d+length] and dst[d-offset:] can overlap, this is
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+ // still OK if offset >= 8.
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+ //
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+ // if length > 16 || offset < 8 || len(dst)-d < 16 {
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+ // goto slowForwardCopy
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+ // }
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+ // copy 16 bytes
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+ // d += length
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+ CMPQ CX, $16
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+ JGT verySlowForwardCopy
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+ CMPQ DX, $8
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+ JLT verySlowForwardCopy
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+ CMPQ R14, $16
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+ JLT verySlowForwardCopy
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+ MOVQ 0(R15), AX
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+ MOVQ AX, 0(DI)
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+ MOVQ 8(R15), BX
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+ MOVQ BX, 8(DI)
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+ ADDQ CX, DI
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+ JMP loop
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+
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verySlowForwardCopy:
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// verySlowForwardCopy is a simple implementation of forward copy. In C
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// parlance, this is a do/while loop instead of a while loop, since we know
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Nigel Tao