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Alpha 通用64位立即数装载

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Alpha 立即数装载方式

  1. 使用立即数装载指令
  2. 使用访存指令从内存装载

Alpha 立即数装载指令

lda

  • 格式：lda ra, imm16(rb)
  • 功能：val(ra) = val(rb) + sign_extend_to_64bit(imm16)

ldah

  • 格式：ldah ra, imm16(rb)
  • 功能：val(ra) = val(rb) + sign_extend_to_64bit(imm16 * 65536)

通用64位立即数装载代码生成

# li64.S
    .text

    .globl    li64
    .enty     li64
    .type     li64, @function
    .set      noreorder
    .set      nomacro
    .set      nomove
    .set      volatile
li64:
    ldah      v0, 0(zero) # highest
    lda       v0, 0(v0)   # higher
    sll       v0, 32, v0
    ldah      v0, 0(v0)   # high
    lda       v0, 0(v0)   # low

    ret       zero, (ra)
    .end      li64
    .size     li64, .-li64

unsigned long imm64;

if ((short) (imm64 >> 0) < 0)
    imm64 += 0x10000ul;
if ((short) (imm64 >> 16) < 0)
    imm64 += 0x100000000ul;
if ((short) (imm64 >> 32) < 0)
    imm64 += 0x1000000000000ul;

short highest = (short) (imm64 >> 48);
short higher = (short) (imm64 >> 32);
short highe = (short) (imm64 >> 16);
short low = (short) imm64;