* {@code x} and {@code y} value pair.
   *
   * @since 20.0
   */
  public static final class LinearTransformationBuilder {

    private final double x1;
    private final double y1;

    private LinearTransformationBuilder(double x1, double y1) {
      this.x1 = x1;
      this.y1 = y1;
    }

    /**
     * Finish building an instance which also maps {@code x = x2} to {@code y = y2}. These values

//
//   twos_complement_eval z = let x1 := z[0] + (z[1] << 64) + (z[2] << 128) + (z[3] << 192) in
//
//                            if x1 & (2^256-1) < 2^255 then x1 & (2^256-1) else (x1 & (2^256-1)) - 2^256

package edwards25519

import "math/bits"

_16_or_more:
	CMPQ AX, $16
	JA   _17_or_more
	MOVOU (R8), X1
	LEAQ -15(DI)(DX*1), DX
loop16:
	MOVOU (DI), X2
	PCMPEQB X1, X2
	PMOVMSKB X2, SI
	CMPQ  SI, $0xffff
	JE   success
	ADDQ $1,DI
	CMPQ DI,DX
	JB loop16
	JMP fail
_17_or_more:
	CMPQ AX, $31
	JA   _32_or_more
	LEAQ 1(DI)(DX*1), DX
	SUBQ AX, DX
	MOVOU -16(R8)(AX*1), X0
	MOVOU (R8), X1
loop17to31:
	MOVOU (DI), X2
	PCMPEQB X1,X2

//
//   twos_complement_eval z = let x1 := z[0] + (z[1] << 64) + (z[2] << 128) + (z[3] << 192) in
//
//                            if x1 & (2^256-1) < 2^255 then x1 & (2^256-1) else (x1 & (2^256-1)) - 2^256

package fiat

import "math/bits"

   * {@code x} and {@code y} value pair.
   *
   * @since 20.0
   */
  public static final class LinearTransformationBuilder {

    private final double x1;
    private final double y1;

    private LinearTransformationBuilder(double x1, double y1) {
      this.x1 = x1;
      this.y1 = y1;
    }

    /**
     * Finish building an instance which also maps {@code x = x2} to {@code y = y2}. These values

			// so the final call to Ldexp will produce under/overflow (0/Inf)
			ae += xe
			break
		}
		if i&1 == 1 {
			a1 *= x1
			ae += xe
		}
		x1 *= x1
		xe <<= 1
		if x1 < .5 {
			x1 += x1
			xe--
		}
	}

	// ans = a1*2**ae
	// if y < 0 { ans = 1 / ans }
	// but in the opposite order
	if y < 0 {
		a1 = 1 / a1
		ae = -ae
	}

func (curve *CurveParams) Double(x1, y1 *big.Int) (*big.Int, *big.Int) {
	// If there is a dedicated constant-time implementation for this curve operation,
	// use that instead of the generic one.
	if specific, ok := matchesSpecificCurve(curve); ok {
		return specific.Double(x1, y1)
	}
	panicIfNotOnCurve(curve, x1, y1)

	z1 := zForAffine(x1, y1)

        itemList.add(new SynonymItem(3, new String[] { "c1" }, new String[] { "C1", "C2" }));
        itemList.add(new SynonymItem(4, new String[] { "x1", "X1" }, new String[] { "x1", "X1" }));
        itemList.add(new SynonymItem(5, new String[] { "y1", "Y1", "y2" }, new String[] { "y1", "Y1", "y2" }));
        synonymFile.synonymItemList = itemList;
    }

    public void test_selectList() {

move_17through32:
	MOVOU	(SI), X0
	MOVOU	-16(SI)(BX*1), X1
	MOVOU	X0, (DI)
	MOVOU	X1, -16(DI)(BX*1)
	RET
move_33through64:
	MOVOU	(SI), X0
	MOVOU	16(SI), X1
	MOVOU	-32(SI)(BX*1), X2
	MOVOU	-16(SI)(BX*1), X3
	MOVOU	X0, (DI)
	MOVOU	X1, 16(DI)
	MOVOU	X2, -32(DI)(BX*1)
	MOVOU	X3, -16(DI)(BX*1)
	RET
move_65through128:
	MOVOU	(SI), X0
	MOVOU	16(SI), X1
	MOVOU	32(SI), X2
	MOVOU	48(SI), X3

	JMP	main(SB)

// When building with -buildmode=c-shared, this symbol is called when the shared
// library is loaded.
TEXT _rt0_riscv64_freebsd_lib(SB),NOSPLIT,$224
	// Preserve callee-save registers, along with X1 (LR).
	MOV	X1, (8*3)(X2)
	MOV	X8, (8*4)(X2)
	MOV	X9, (8*5)(X2)
	MOV	X18, (8*6)(X2)
	MOV	X19, (8*7)(X2)
	MOV	X20, (8*8)(X2)
	MOV	X21, (8*9)(X2)
	MOV	X22, (8*10)(X2)
	MOV	X23, (8*11)(X2)
	MOV	X24, (8*12)(X2)