circom/c/buildasm/neg.asm.ejs

<% function negS() { %>
        neg    eax
        jo     neg_manageOverflow   ; Check if overflow. (0x80000000 is the only case)

        mov    [rdi], rax           ; not necessary to adjust so just save and return
        ret

neg_manageOverflow:                 ; Do the operation in 64 bits
        push   rsi
        movsx  rsi, eax
        neg    rsi
        call   rawCopyS2L
        pop    rsi
        ret
<% } %>

<% function negL() { %>
        add rdi, 8
        add rsi, 8
        call rawNegL
        sub rdi, 8
        sub rsi, 8
        ret
<% } %>

;;;;;;;;;;;;;;;;;;;;;;
; neg
;;;;;;;;;;;;;;;;;;;;;;
; Adds two elements of any kind
; Params:
;   rsi <= Pointer to element to be negated
;   rdi <= Pointer to result
;   [rdi] = -[rsi]
;;;;;;;;;;;;;;;;;;;;;;
<%=name%>_neg:
        mov    rax, [rsi]
        bt     rax, 63          ; Check if is short first operand
        jc     neg_l

neg_s:                          ; Operand is short
<%=     negS()       %>


neg_l:
        mov [rdi], rax          ; Copy the type
<%=     negL()       %>


;;;;;;;;;;;;;;;;;;;;;;
; rawNeg
;;;;;;;;;;;;;;;;;;;;;;
; Negates a value
; Params:
;   rdi <= Pointer to the long data of result
;   rsi <= Pointer to the long data of element 1
;
;   [rdi] = - [rsi]
;;;;;;;;;;;;;;;;;;;;;;
rawNegL:
        ; Compare is zero

        xor rax, rax
<% for (let i=0; i<n64; i++) { %>
        cmp [rsi + <%=i*8%>], rax
        jnz doNegate
<% } %>
        ; it's zero so just set to zero
<% for (let i=0; i<n64; i++) { %>
        mov [rdi + <%=i*8%>], rax
<% } %>
        ret
doNegate:
<% for (let i=0; i<n64; i++) { %>
        mov rax, [q + <%=i*8%>]
        <%= i==0 ? "sub" : "sbb" %> rax, [rsi + <%=i*8%>]
        mov [rdi + <%=i*8%>], rax
<% } %>
        ret